Removed tracks and re-adding tracks

[Noam-Bendelac]

• DB changes
  • Add "re-add" actions to separate chat event actions and situated chat event actions 7ef96f0
  • Also make situated chat event action required, with a "comment" option? Similar idea for separate chat event action 1fc89d3
  • removedTracks array in playlist 7ef96f0
    • removedBy field
    • Cache certain Spotify data like album, name, artist (14c8dc2); but first refactor to simplify API response as described in Move some processing of Spotify data to the backend #71 394add2
• Backend changes
  • PUT .../:trackId/removed for both removal and re-adding? What should POST .../:playlistId/tracks/ do (babb241)? Re-add track when track exists in removed state #44 7ef96f0
  • Make .../:trackId/chat and similar endpoints work for both present tracks and removed tracks
  • Changes required for above DB changes
• Rename instances of "tracks" to "present tracks"? To differentiate from removed tracks
• Frontend rendering
  • New table section
  • Table headers? "Removed tracks" heading? "Removed By" header for the "Added By" column?
• Frontend "re-add" state in modificationState
• User guards disallowing actions depending on track state
  • Can't add search result if it's already an existing track (show it, but disable the add button) How to prevent adding existing track #45
  • Should search result's add button be disabled if it's already a removed track? Or should it do the same thing as clicking the removed track's re-add button? Re-add track when track exists in removed state #44