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/keyboard.js

@@ -65,7 +65,13 @@ class Keyboard{
 	}
 	keyEvent(event){
 		var key = event.key.toLowerCase()
-		if(key === "escape" || key === "backspace" || key === "tab"){
+		if(
+			key === "escape" ||
+			key === "backspace" ||
+			key === "tab" ||
+			key === "contextmenu" ||
+			key === "alt"
+		){
 			event.preventDefault()
 		}
 		if(!event.repeat){