Extensions should support enough functionality to be useful

[decarbonization]

The extensions system in The Listening Room is pretty anemic right now. The following line items should be addressed so that TLR can be meaningfully extended outside of its core codebase.

Extension Points

• Add context menu items
• Add search results
• Add a left pane tab
• Add a right pane tab

Library Integration

• Efficient paginated query system
• Query songs/albums/artists
• Query plays/skips
• Edit and remove songs
  • Edit audio file tags
• Add songs

Playback Integration

• Playback engine coordination
• Activate custom playback engine
• Register custom playback engine for specific URL scheme(s)

Player Integration

• Read and observe playback state
• Playback transport control (play/pause, skip, etc)
• Read up next queue
• Change up next queue
• Start playback

Clerical

• Make IDs opaque, support arbitrary values when called for
• Move extension SDK into its own repo