Merge branch 'release/0.19.0'

changes/changelog.d/722.bugfix

-Fixed non-transparent background for volume range on Firefox (#722)
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changes/changelog.d/725.enhancement

-Merged artist/album buttons with title text on artist and album pages (#725)

changes/changelog.d/740.bugfix

-Do not consider tracks as duplicates during import if they have different positions (#740)

changes/changelog.d/747.feature

-Support embedding full artist discographies (#747)

changes/changelog.d/748.enhancement

-Labels for privacy levels are now consistently grabbed from a common source instead of being hardcoded everytime they are needed.

changes/changelog.d/752.feature

-Support OAuth2 authorization for better integration with third-party apps (#752)

changes/changelog.d/754.bugfix

-Add missing command from contributing file (#754)

changes/changelog.d/758.bugfix

-Ensure all our ActivityPub fetches are authenticated (#758)

changes/changelog.d/768.enhancement

-Descriptions will now be shown underneath user libraries (#768)
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changes/changelog.d/770.doc

-Document how to use Redis over unix sockets (#770)

changes/changelog.d/772.bugfix

-Prevent skipping on file import if album_mbid is different (#772)

changes/changelog.d/776.enhancement

-Don't store unhandled ActivityPub messages in database (#776)

changes/changelog.d/777.enhancement

-Added a prune_library management command to remove obsolete metadata from the database (#777)

changes/changelog.d/781.enhancement

-Added a `check_inplace_files` management command to remove purge the database from references to in-place imported files that don't exist on disk anymore (#781)

changes/changelog.d/782.bugfix

-Better handling of featuring/multi-artist tracks tagged with MusicBrainz (#782)

changes/changelog.d/784.feature

-Display a confirmation dialog when adding duplicate songs to a playlist (#784)

changes/changelog.d/791.bugfix

-Fixed overflowing input on account detail page (#791)

changes/changelog.d/795.bugfix

-Fixed cover not showing in queue/player when playing tracks from "albums" tab (#795)

changes/changelog.d/798.bugfix

-Allow users with dots in their usernames to request a subsonic password (#798)

changes/changelog.d/799.enhancement

-Removed broken/instable lyrics feature (#799)