Renamed ImageRepresentationDisk::getImage() to ImageRepresentationDisk::getWeaklyTypedPointer() for more consistency with the other representations.
Added a UML component diagram of the main CAMPVis concepts as well as a UML class diagram of the ImageData API.

Removed generation of obsolete gen_converterregistration.h file through CMake since converter registration now entirely relies on explicit template specialization.

refs #386

refs #386

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

* Added OpenGL thread guard to image conversions to ImageRepresentationGL.

refs #474
refs #553

Removed all code fragments in core code that was ITK specific (conversion from/to GenericImageRepresentationItk). The functionality was replaced by the new conversion functors in imagerepresentationconversionitk.h and imagerepresentationconversionitk.cpp.

refs #553
refs #474

Conversions between image representations are now managed at one central place: The ImageRepresentationConverter singleton uses the proven and established registration through static template instantiation idiom to register conversion functors during static initialization. Therefore, the ConversionFunctionRegistrar registers a conversion functor to a target representation type.

As proof-of-concept implementation, the former conversion API through T::tryConvertFrom, where T is a specific image representation, has been converted to the new API and merged into imagerepresentationconversioncore.h providing a conversion functor for each campvis-core representation.

Furthermore, implemented conversion from ImageRepresentationGL to GenericImageRepresentationLocal<>.

refs #553
refs #474