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/css/view.css

@@ -377,3 +377,29 @@ kbd{
 	font-size: 1.1em;
 	color: #d00;
 }
+.customdon-div{
+	display: flex;
+	justify-content: center;
+	align-items: center;
+	text-align: right;
+}
+.customdon-canvas{
+	max-width: 40vw;
+}
+.customdon-div label{
+	display: block;
+	padding: 0.3em;
+}
+.customdon-div input[type="color"]{
+	font-size: inherit;
+	width: 2.6em;
+	height: 1.6em;
+	padding: 0 0.1em;
+	vertical-align: middle;
+}
+.customdon-reset{
+	width: 100%;
+	font-family: inherit;
+	font-size: 1em;
+	padding: 0.2em;
+}