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/views/account.html

@@ -7,6 +7,20 @@
 				<div class="displayname-hint"></div>
 				<input type="text" class="displayname" maxlength="25">
 			</div>
+			<div class="customdon-div">
+				<canvas class="customdon-canvas" width="254" height="184"></canvas>
+				<div>
+					<label>
+						<input type="color" class="customdon-bodyfill">
+					</label>
+					<label>
+						<input type="color" class="customdon-facefill">
+					</label>
+					<label>
+						<input type="button" class="customdon-reset" value="Reset">
+					</label>
+				</div>
+			</div>
 			<form class="accountpass-form">
 				<div>
 					<div class="accountpass-btn taibtn stroke-sub link-btn"></div>