Clean up the interface.

* All clickable items are javascript-only anchors/buttons, so no more
  href="#" that scroll to the top when clicked.
  * These items all feature the "pointer" cursor.
* "Game Over" modal is now unclosable.
* Fix display of ul's within a ul.list-group.
* Same colour for all modal closing buttons: gray (which should be the
  colour bootstrap assigns to btn-default, but for some reason it
  didn't, so put it in manually).