David Frank authored Jun 23, 2020 and Tobias Lasser committed Jun 23, 2020

- Add Abstract class DetectorDescriptor, which is derived from DataDescriptor (Support ray generation from a given pose and detector pixel and given pose and voxel)
- Add first derived class of DetectorDescriptor: PlanarDetectorDescriptor
- Add usage of DetectorDescriptor in Projectors (remove dependency to geometry, ray generation is only handled by DetectorDescriptor, adapt tests)
- Restructure tests of CUDA projectors to make failing tests more readable