Add custom Don

- Registered users can customise the colour of their Don and it will appear for other players
- Bug fixes:
  - Add lyrics checkbox to admin page
  - 2P shows above "creative" or "with lyrics" labels
  - Prevent accidental alt and menu keyboard presses from triggering browser menus
  - Fixed mouse hitboxes on difficulty selection
  - Clean cached sounds and lyrics when another song is loading
  - Fixed debug jumping to the top-left of the screen when hidden
  - Fixed server volume not being applied to songs

- Use inline "#LYRIC" lines in tja files
- "LYRICS:" in tja metadata can point to a vtt file, this overrides "#LYRIC"

- Place these in your .git/hooks/ directory

- Fix subtitle if the previously selected song had the same title