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/loader.js

@@ -178,6 +178,7 @@ class Loader{
 						account.loggedIn = true
 						account.username = response.username
 						account.displayName = response.display_name
+						account.don = response.don
 						scoreStorage.load(response.scores)
 						pageEvents.send("login", account.username)
 					}
@@ -236,7 +237,8 @@ class Loader{
 						})
 						p2.send("invite", {
 							id: location.hash.slice(1).toLowerCase(),
-							name: account.loggedIn ? account.displayName : null
+							name: account.loggedIn ? account.displayName : null,
+							don: account.loggedIn ? account.don : null
 						})
 						setTimeout(() => {
 							if(p2.socket.readyState !== 1){