Support adding songs without recompiling the mod

[rigdern]

Adding a song requires 3 pieces of information:

• The song ID
• The Spotify analysis file for the song
• ShiftTimestampsSeconds. The number of seconds by which to shift the Spotify analysis timestamps so that they're aligned with those of the Beat Saber song.

Potential solutions

• To add a song, create a JSON file called <song-id.json> in InfiniteBeatSaber/songs. It has these keys:
  • shiftTimestampsSeconds
  • spotifyAnalysis: The value should be the contents of the Spotify analysis file (for example Spotify analysis files, see SpotifyAnalyses/)

Other notes

• Modifying a song's Info.dat changes its hash and, consequently, ID. This is used by Beat Saver when submitting scores to the leaderboard.
• I'm not sure if adding new files to a song's folder would have any unintentional effects. I don't think it affects the song's hash/ID. It would be good to double check.

See also

• Support a field for specifying Spotify analysis file path in Info.plist of custom maps #16