Write all tags with exiftool instead of relying on RawTherapee

All Exif and XMP tags are currently only written to the DNG file and the tags of the final TIFF depend on RawTherapee correctly writing them during conversion. This can sometimes fail, and TIFF files that are written directly by the library therefore don't have any EXIF tags applied.

The solution would be to write EXIF tags explicitly to all TIFF files using Exiftool or similar.

This may allow to skip using the PiDNG library all-together since it has trouble writing EXIF tags correctly.