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

public/src/js/scorestorage.js

@@ -285,6 +285,7 @@ class ScoreStorage{
 						account.loggedIn = false
 						delete account.username
 						delete account.displayName
+						delete account.don
 						this.load()
 						pageEvents.send("logout")
 						return Promise.reject()