Release 3.0.3

[matthijskooijman]

These are the final changes to release 3.0.3.

The release procedure, as proposed in #686 (comment) is as follows:

1. Document all changes in the NEWS.md file
2. Make a commit that sets the version number in src/hamster/VERSION and version number and release date in NEWS.md
3. Tag that commit (or the merge commit if merged through a PR)
4. Create a github release with the notes from the NEWS file, and attach the flatpak build.
5. Create a new commit that removes the version number again and adds a ## Unreleased changes header to NEWS.md and reset src/hamster/VERSION to unreleased.

This PR handles 1. and 2. I already have a commit locally for 5. I plan to do merge this PR and do 3. and 4. tonight.

If there's anyone with final remarks before the release, now would be the time :-) @rhertzog @DirkHoffmann @GeraldJansen @mwilck

I collected a nice of TODO list of things that I would have liked to fix before this release, but have left out in the interest of progress (mostly wrt to release automation, flatpak stuff, etc.), or things that do not need to be in the release (e.g. documentation updates). @DirkHoffmann suggested we keep up the momentum and do a followup release with such improvements around Christmas, which I think is a good idea!

[github-actions]

Automatically generated build artifacts for commit e721b75 (note: these links will expire after some time):

• Flatpak application: ⏬ Download

---

To test this PR, download and unzip the flatpak application above and then install with:

flatpak install Hamster.flatpak

[github-actions]

Automatically generated build artifacts for commit 71d0f71 (note: these links will expire after some time):

• Flatpak application: ⏬ Download

---

To test this PR, download and unzip the flatpak application above and then install with:

flatpak install Hamster.flatpak

[matthijskooijman]

While testing the Debian package, I discovered that the src/hamster/VERSION file introduced by this commit has a trailing newline, which ended up in the generated defs.py, breaking compilation. I've now force pushed with this trailing newline omitted, but I've made a note to fix the code that reads the VERSION file to strip whitespace as a more reliable fix.

[matthijskooijman]

With that change, the Debian package seems to build and work fine, so I'm going to merge this and create the release! :-D

[matthijskooijman]

I've just pushed 9eb80bc (directly to master) to reset the git tree for development again (i.e. remove 3.0.3 from VERSION).