Unify flat correction and sinogram correction

fixes #34
Merge pull request #35 from ufo-kit/unify-flat-corrections

Unify flat correction and sinogram correction
Replace with GPU version
Merge pull request #37 from ufo-kit/gpu-roi

Change CPU version of ROI by GPU
Add basic median filter task
Remove unused value
Look for libtiff4 via pkg-config
Integration of the UfoIR