uamp v0.7.0

This quite big release adds support for albums and artist grouping on the server side. This improves the grouping inside GUI. There are also many bugfixes and nice features on both server and client side.

Breaking changes

Majority of users are unlikely to be affected.

On first startup after this update, uamp will fail to load cached metadata from
library and so it will also make all playlists empty. You will have to reload
your library. Some cached images will also be no longer used, so you can
delete the image cache at ~/.cache/uamp/ if you would like to make sure that
there are no unused cached files.

The http api has also changed to reflect these changes. The set-all sse now
contains albums and artists and song now has nullable fields and artists and
genres is array.

• Rework library format:
  • Properly represent missing metadata of songs.
  • Add support for album artists
  • Uamp can now work with albums and artists.

New features

• Uamp can now work with album artists.
• Each song can now have multiple artists.
• Each song can now have multiple genres.
• Query for empty string is interpreted as that property should not be set.
• Add new control message to retain only some songs in playlist with
  playlist-retain.
• Add option to end the current playlist with end-playlist.
• Add control message remove-playlist that can remove playlist at the given
  index.
• Add option to negate matching modes with ^.
• Support negation in filter with ^.

GUI

• Add progress bar dragging
• Add context menus (song, playlist, album, artist)
• Add keyboard shortcuts
• Tweak design

Changes

• Add new id control messages InsertIntoPlaylist and RemoveFromPlaylist.
• Unify sse queue and play-next into insert-into-playlist.
• Add new sse remove-from-playlist.
• The post endpoint for /api/ctrl now also supports array of messages.
• Improve logging. Some of what was previously error is now warning. Most
  log messages that come from uamp will now also show source location.
• Add POST api to check control message at /api/check_ctrl.
• Add new sse remove-playlist.
• Uamp now sends all sse names in set-all.

Fixes

• Fix panic in mix after into empty playlist.
• Uamp now properly supports image lookup for songs with missing album, artist,
  and title.
• Fix potential issues when current or prefetched song was removed from
  library.
• Properly wait for graceful shutdown of connections when closing uamp.
• Fix filter parsing.

GUI

• Fix volume overwrite on startup
• Fix album hover effect
• Fix history API