xmp tags: compress bigger binary fields
Merge branch 'master' into zxmp
make XMP tag compression a config option
Merge branch 'zxmp'
Merge branch 'master' into duplicate_fix
xmp files: make parsing of uncompressed data more bullet proof
Merge branch 'duplicate_fix' of ssh://github.com/darktable-org/darktable into duplicate_fix
image duplicates: on DELETE of last duplicate also delete all orphaned xmp files

orphaned xmp files represent previously REMOVED duplicates. they are kept so one can
reimport the folder and fully reconstruct all edits. however, when the source data
file has been deleted there is no reason to keep those sidecar files.