Refactor reference counting

* Added OrCombinedPointPredicate implementation
* Updated default settings in PredicateDemoCarotid2 pipeline

(Apparently, I really need some rest...)

Itk reader

ITK Image reader that supports many more image formats.
Example usage edited into the itkfilterdemo pipeline.

 * supports all file formats that can be read via ITK
 * does not support image series

* SliceExtractor FitToWindow property defaults to true to mimic old behavior per default
* PointPredicateRenderArea renders y axis label

* Now supports optional scaling and offset of image
* Added properties for geometry render style and size
* Fixed some scribbling-related bugs

Slice extractor scribbe fix

as discussed

Datastructures

basic datastructures for Matrix and position data

Slicerenderer2d

slice renderer that applies transfer function, clips image and/or inverts axes.
tested only with grayscale input images, but should support color and images as well.

* undo changes to .gitignore (regarding SWIG temporary files)
* moved implementation of PositionData and TransformData from header to source file

Mhdreader fix

Sorry for the huge commit - only couple of files changed (see commit) :-(

Fixed timing issue in CampVisPainter that led CampVisPainter::paint() being called before CampVisPainter::init(). CampVisPainter::paint() now ensures the class (and in particular the shader) to be correctly initialized.

fixes #564

Initial implementation of a Lua scripting layer

Over the last several months a scripting layer that allows pipelines to be defined in Lua has been developed. It uses SWIG to generate Lua modules with bindings for CAMPVis classes. It is an opt-in feature, and tries to be as non-intrusive to standard CAMPVis code as possible.

The implementation of the scripting layer has reached a state where it's possible to write fully-functional pipelines in Lua. In fact, 2 existing pipelines have been reimplemented in Lua for testing purposes and added to the project. In my opinion, this marks a good point to merge the initial implementation into the development branch — that would make it easier to test and improve it.

Naturally, there are still many rough edges that should eventually be dealt with, but they can be addressed separately as new features:
- bindings coverage is rather low
- Lua pipelines currently need to be statically registered
- pipeline definition syntax could be streamlined (e.g. by getting rid of the `instance` global variable)

The CMake-enabled version of Lua that CAMPVis' scripting layer uses
hasn't been updated in a while. Synchronise it with upstream now that
we're getting ready to merge the `swig` branch in.

References #1

`scripting/testapp.cpp` contains a simple console application that was
used to test CAMPVis' scripting layer before it was ready for
integration with the main GUI application. Now that Lua pipelines can be
registered and executed the same way regular ones are, the test
application is no longer needed. Consequently, this commit removes it
from the project.

References #1

Glue classes that live in the `scripting/glue` directory were mostly
undocumented, and the documentation of LuaPipeline was incomplete.

Improve the documentation of LuaPipeline and LuaVmState. Document
LuaTable, RegularLuaTable and GlobalLuaTable from the `scripting/glue`
directory.

References #1

Starting with commit d6fec679, pipelines need to provide their own light
source to function properly. Lua pipelines didn't, which caused them to
fail to render.

Add a SWIG wrapper for LightSourceProvider to make it accessible from
Lua. Instantiate and attach a light source in existing Lua pipelines.

References #1

Commit 293d43dd introduced breaking changes to the way invalidation
levels are handled. As a result, property and processor-related bindings
failed to compile.

Update all SWIG bindings affected by the above problem to make them
compatible with the current property and processor-related APIs.

References #1

LuaDist, the CMake-enabled distribution of Lua that the scripting
feature uses on Windows, provides several targets (lua, luac, wlua) for
which there's not much use in CAMPVis. This commit hides them from the
target list to make project files generated by CMake cleaner.

References #1

If CAMPVIS_BUILD_LIB_LUA was set but the Lua Git submodule wasn't checked
out, the user would get a generic "could not find CMakeLists.txt" error
message which wasn't of much help.

Log a custom error message that provides a hint how to fix the problem in
the above situation.

References #1

The FindLua CMake script would previously set LUA_FOUND if the directory
containing the source code of Lua existed without checking if it was
actually part of the build. This could lead to compilation errors if
CAMPVIS_BUILD_LIB_LUA was disabled.

Add an additional check to FindLua to only set LUA_FOUND if
CAMPVIS_BUILD_LIB_LUA is ON and the directory containing the source code
of Lua exists.

References #1

Scripting was so far enabled by default on the `swig` branch to make its
development easier. However, it should be an opt-in feature once it's
merged in. As that time is quickly approaching, the scripting feature has
been disabled by default.

References #1

Early in the development of the scripting feature the
`campvis-scripting-test` target was used to test bindings generated by
SWIG. Now that pipelines defined in Lua have been integrated into the
main application (where the bindings they use can be tested much more
thoroughly) the console test application is no longer needed and has
been removed.

References #1

SWIG wrappers for siglot only supported unary signals until now. This
commit adds support for all remaining signal arities to make it possible
to connect to arbitrary signals from Lua.

The implementation makes heavy use of templates but, due to the
limitations of VS 2010 (no variadic templates), still contains lots of
duplicated boilerplate code.

`sigslot.i` has been moved from `scripting/` to `ext/sigslot/` to keep
it close to the code it's wrapping.

References #1

Up until now it wasn't possible to manually disconnect slots defined in
Lua: they could only be disconnected automatically when their
corresponding signals were destroyed.

Add a special `disconnect` method to sigslot's Lua wrapper that makes it
possible to manually disconnect slots defined in Lua.

References #1