pyacoustid: upstream update and various packaging improvements

[Lars Kruse <lists@sumpfralle.de>]

Hello,

I am a member of the DPMT, but no DD or DM.
This is supposed to be my first package upload within the DPMT, thus please be
patient, in case I misunderstand the procedure.

My proposed changes of the package include the following:
* migrate from git-dpm to gbp
* update upstream (closing all open bugs)
* add initial autopkgtests
* updates of policy version and compat level

I prepared a merge request with my changes:
  https://salsa.debian.org/python-team/modules/pyacoustid/merge_requests/1

The git-dpm migration requires a branch renaming ("master" -> "debian/master").
The upstream update requires an update of the upstream branch.
Thus the merge request is not fully self-contained. See my forked repository for
the complete updated environment:
  https://salsa.debian.org/sumpfralle-guest/pyacoustid/

I am not sure, how to proceed now, but I could imagine the following steps:
1) someone takes the time to review my changes (maybe followed by fixes from me)
2) I push my changes (including a debian/??? version tag) to the
   packaging repository within DPMT (and delete my forked repository)
3) the reviewer sponsors the upload of the package

I am looking forward to your comments or reviews.

Cheers,
Lars