Refactor opengl api

See merge request !98

* Tied tgt::OpenGLJobProcessor and tgt::OpenGLGarbageCollector closer together regarding OpenGL garbage collection
* AutoEvaluationPipeline checks for valid OpenGL state after each processor call (only in debug)

* Fixed AutoEvaluationPipeline missing some updates
* Fixed AutoEvaluationPipeline::executePipeline() to execute processors too often
* Fixed ParticleFlowRenderer overwriting bound FBO
* Added Debug checks to tgt::FramebufferObject and tgt::Shader to print warnings when FBO/Shader activation would overwrite an already active FBO/Shader

* Renamed OpenGLJobProcessor::iKnowWhatImDoingGetArbitraryContext() to OpenGLJobProcessor::getContext()
* Adjusted headers and method calls in various files

Let tgt::OpenGLGarbageCollector issue its garbage collection request to tgt::OpenGLJobProcessor to get this done in a background thread.

Moved AbstractJob and OpenGLJobProcessor from campvis-core to tgt and adapted and cleaned up all necessary includes/references.

The new OpenGL wrapping API allows for full multi-threaded access to OpenGL contexts. Instead of one single thread scheduling all OpenGL jobs for all contexts, the new GlContextManager allows for OpenGL access from multiple threads while ensuring that each OpenGL context is acquired by only one thread at a time.

Detailed list of changes:
* tgt::GlContextManager keeping track of which threads acquire which OpenGL contexts and which threads currently have a context acquired.
* OpenGLJobProcessor does no longer schedules and execute the OpenGL calls for all existing contexts, but only for one single context that can be used for background tasks or other jobs that explicitly need a valid OpenGL context.
* AbstractPipeline now implements the Runnable interface and thus runs in it's own thread. This thread also owns the pipeline's OpenGL context.
* AbstractPipeline has a new pure virtual method executePipeline() that has to perform all computations done by the pipeline.
* AbstractPipeline now takes directly care of calling Painter::paint() of the pipeline's canvas (instead of signalling the Painter). However, the Painter interface needs further cleanup.
* AutoEvaluationPipeline was adapted to the new AbstractPipeline API, hence executing processors is no longer delegated to the OpenGLJobProcessor or the SimpleJobProcessor but entirely done in AutoEvaluationPipeline::executePipeline() and thus in the pipeline's thread.
* Adjusted CampVisApplication, DataContainerInspectorWidget, and GeometryTransferFunctionEditor to the new API.

* Fixed AdvOptimizedRaycaster::updateProperties overload.

Advanced raycasting

+ Changes are done to the code.

See merge request !72

Merged Morteza's changes into one single commit.

Columbia fixes

See merge request !96

Added directories of various needed resources (textures, sampledata) to the CampvisShaderDirectories CMake variable, which is used for deployment. Replaced various occurences of CAMPVIS_SOURCE_DIR with ShdrMgr.completePath().

* Fixed GenericPointerData::getData() implementation
* Improved input data handling in RenderTargetCompositor: Will also show something if only one of the two inputs are set
* removed obsolete GlReductionTest pipeline

* Added optional picking information to GeometryData API
* GeometryRenderer processor renders the picking information into a separate texture if present
* geometrydata.h contains a stub for a possible rewrite of the API (more flexible buffer layout)

Made calls to ImageData::tryPerformConversion() mutually exclusive to avoid concurrent conversions to the same target data type.

Particle visualization

See merge request !95

Updated VectorFieldDemo pipeline to allow the user to choose between arrow- and particle visualization.

* Introducing ParticleFlowRenderer processor implementing a particle simulation using OpenGL transform feedback
* Added tgt::Shader::selectSubroutine()
* Added tgt::VertexArrayObject::getId()

Core updates

Various updates to the base library, cherry-picked from the biopsy-workflow-gui branch. Most notably:

* new AbstractJob instance taking C++11 functionals in the constructor
* new QtJobProcessor singleton for executing jobs in the Qt GUI thread
* new StatusProperty and StatusPropertyWidget to display status information as color+text
* ButtonProperty forwards clicks to its shared properties
* s_changed signal of properties is only fired if the value actually has changed
* MatrixProcessor fix for endless loops occuring when a formula uses a matrix that is computed by that same formula and that is put into the data container
* various accessors to internals of MainWindow and AbstractPipeline

See merge request !93

* Updated CMake scripts to work with new CMake 3 and TBB 4.3

core API change: properties don't emit s_changed signal if setValue() is called with the current value

* new QtJobProcessor singleton: used to execute jobs in the Qt thread
* CampvisApplication now has a map to obtain the window for a pipeline

* AbstractPipeline offers getter for the canvas to execute jobs in the pipeline's OpenGL context
* PropertyCollectionWidget adds a spacer element at the end to prevent element stretching when there is too much free space
* job.h offers new CallFunctionObjectJob to create jobs on the fly using lambda functions (the respective makeJob and makeJobOnHeap are inlined to prevent linker errors)