Instead of using the "just_audio_windows" and "just_audio_mpv" packages
for Windows and Linux, we are now using "just_audio_media_kit", so that
the audio player is working reliable on these platforms.
Note: We have to adjust the Flatpak, to include the dependencies which
are required on Linux.
- Adjust "Release" section in contributing guide.
- Disable "X" datasource, since it is not working after the latest API
adjustments.
- Update "version" key and "msix_config.msix_version" key in
"pubspec.yaml" file.
- Change user in "AddSourceReddit" widget help text.
- Enable macOS App Sandbox.
- Adjust logo for Windows version.