Small fixes

[matthijskooijman]

Just a few small fixes that I noticed during the 3.0.3 release, that could be made or investigated:

• Move dbus service files into data/ or another subdir for cleanup. Also maybe move the flatpak file, see Flatpak improvements #743.
• Drop LIBDIR from defs.py.in (for Debian reproducible builds), and maybe others too (only VERSION and DATADIR seems used).
• Is data/hamster.db actually used? Does it define the initial db schema, or is it leftover from an old version? Yes, still used.
• See if we can remove distutils import (it seems deprecated, and according to lintian removed in Python 3.12, though it does still seem to work in 3.12 so far).
• Strip whitespace from VERSION to allow newlines (Release 3.0.3 #742 (comment))
• Fix py3.6 compatibility for subprocess.run, see Improved versioning #738 (review)

[matthijskooijman]

Is data/hamster.db actually used? Does it define the initial db schema, or is it leftover from an old version?

Turns out it is, this bit of code copies the empty hamster.db into place when no database exists yet. So nothing to be done there.