Fixes -Wsign-compare

Fixes -Wignored-qualifiers

Fixes -Wswitch

Fixes -Wreorder

Previously, QtCanvas' init() would call show() on its underlying widget
and cause it to appear as a top-level window for a split second, before
the canvas was docked. To avoid this flicker, show() is now only called
on the canvas after it's been added to the MDI area.

Previously, when an MDI window was being dragged very fast and its state
changed from docked to floating (or vice versa), it wouldn't be placed
under the cursor, but instead some way behind it (with regards to the
drag direction). This happened because we decided where to place the
window's based on its last position in its previous state. Now we use
the cursor's position to calculate the window's new position, which
fixes the problem.

PipelineMdiSubWindow has been renamed MdiDockedWindow, and
refactored to make it easier to use it with arbitrary widgets.

To better group MDI-related classes, all of them have been moved to the
´gui/mdi´ directory.

VisualizationPipelineWidget has been renamed MdiFloatingWindow, and
refactored to make it easier to use it with arbitrary widgets.

VisualizationPipelineWrapper has been renamed MdiDockArea, and refactored
to make it easier to use it with arbitrary widgets. It now inherits from
QMdiArea, which removes an unnecessary layer of indirection. Moreover, it
creates MDI subwindows and floating windows only if necessary, i.e. when
a widget stored in it changes state.

Work on Issue #44: Removed GLContext interface and merged functionality into GlCanvas. Introducing abstract (Qt-free) tgt::GlContextManager interface, being implemented by tgt::QtContextManager. Further clean up of related code.

CampvisApplication manages multiple DataContainers, updated PipelineTreeWidget to show correct DataContainer/Pipeline/Processor hierarchy

fixed VolumeExplorer::updateProperties()

Removing TBB library from /ext making it fully external (user has to install TBB himself). Adapted CMake files. Adapted include directions

Refactored DataNameProperty: Got rid of issueWrite() and connect(). Automatic invalidation of connected (shared) DataNameProperties is now delegated to AutoEvaluationPipeline.
ATTENTION: needs TBB 4.2 (not yet in repository, will be changed later)

Refactoring pipeline concept #7: Implemented automatic parsing of include files for pipeline registration

Refactoring pipeline concept #6: Introducing automatic creating of pipeline registration file using CMake

Refactoring pipeline concept #5: Moved Pipeline registration to modules module and gen_pipelineregistration.h which will soon be generated by CMake.

Refactoring pipeline concept #4: (Almost) got rid of hard pipeline definition in campvis.cpp. Implemented console argument parsing in CampvisApplication dynamically adding the pipelines listed as arguments