* added computation of difference image to SimilarityMeasure
 * fixed possible out of bounds access in datacontainerinspectorwidget.cpp
 * added assertions to ImageRepresentationGL constructor

* OpenGl based reduction in core tools
* SimilarityMeasure processor stub

* Fixed pointer inconsistencies in ScopedTypedData and ScopedRepresentation

Conflicts:
	application/gui/datacontainerinspectorcanvas.cpp

+ some minor beautifications/fixes

Fixed tgt::FramebufferObject to work with Intel GPUs (for some reason, the Intel OpenGL driver fails generating and binding FBOs when using the core (non-EXT) GL functions).

+ Using passthrough.vert and geometryrenderer.frag instead of the meshGeometryRenderer.vert and meshgeometryrenderer.frag
+ adding comments for the destroy function of GeometryTextureInfo and why to use it.
+ Change the depth buffer size changing part of Paint() function in datacontainerinspectorcanvas checking part.
+ Delete the commented codes which are not necessary.
+ Fix the opening braces and removing the redundant parts and only for debugging parts.
+ DVRVis and volumerendererdemo default file is revereted to the original locations.
+ Revert the shaders to the original ones.
+ StartMouseDrag and EndMouseDrag functions of the trackball are replaced with mousePress and mouseRelease.

- Delete the meshGeometryRenderer.vert and meshgeometryrenderer.frag.

Merge branch 'OpenGL3-core-refactoring' of /mnt/bigone/git/repositories/berge/campvis into development

fixed CMake error introduced in e1551c26: CAMPVIS_HAS_MODULE_XYZ was no longer defined by CMake

Cleaned up and slightly revised GeometryData API. Cleared the way for non-value semantics. Introducing GeometryDataFactory, a collection of static methods to create standard geometric primitives.

work on Issue #88: cleaned up VertexArrayObject interface. It's now simpler and more straight-forward.

* Adapted shaders to new texture formats

+ Moving the geomteryshader vertex and fragment shader to application folder as they belong to it.
+ Removing unndeeded shader code.
+ Opening braces convention is considered for datacontainerinspectorcanvas.cpp and datacontainerinspectorcanvas.h  also.
+ Reusing textues for color and depth buffers instead of creating and deleting them.
+ adding gettrackball function to trackball event handler.
+ modifying resetcontent, mouse events in datacontainerinspectorcanvas class
+ using one depth buffer for datacontainerinspectorcanvas instead of one for every color buffer
+ using one frame buffer for whole datacontainerinspectorcanvas instead of one for every frame

Also link only to needed ITK modules to reduce linking time.

Issue #250: Make Qt dependency in tgt optional (not needed when building CAMPVis without application)

removed preprocessing dependency from vis module (former dependency was only due to some deprecated code)

 * Finished implementation of empty space skipping
 * Renamed Adaptive Step Size to Intersection Refinement (which is more precise in terms of what it's doing)

No modules were previously enabled by default. As a result, the
application wasn't very useful in the default configuration.

Enable the Vis module by default to make the CAMPVis application
functional out of the box. Additional modules can be marked as default
in the future using the mechanism (SET_DEFAULT_MODULES) introduced in
this commit.

Closes #144