Add music functionality

[Ilwyd]

What has been done?

Functionality is mostly complete, I just have some refactoring and commenting to do. Will update once it's ready.

• Unlocking songs
  • Automatically unlocking default songs (70 total)
  • Send message with song name when unlocking, except when unlocking the default songs
  • Unlocking songs by region
  • Unlocking song by polygon area
    • Implement SimplePolygonArea
    • Implement on_enter_simple_polygon_area plugin
• Playing songs
  • Changing songs manually
  • Changing songs manually from the playlist
  • Changing to songs when entering a region (was already implemented)
  • Changing to songs when entering a polygon area
• Playlist functionality
  • Rearranging songs in the playlist
  • Adding songs to the playlist
  • Removing songs from the playlist
  • Add clear playlist button
  • Enabling the playlist
  • Enabling shuffle on the playlist
• Implement in-packet SoundSongEndMessage
  • Implement on_song_end plugin
  • Automatically change to the next song when the previous one ends, based on playlist / shuffle varbits or the region / area the player is in
• Add commands
  • Add unlocksong command to unlock specific songs
  • Add resettracks command to re-lock all songs
  • Add unlockallttracks command to unlock all songs

Has your code been documented?

Yes