Implement a very simple toolbar for the host to use

This is a small clickable gear at the upper-right, that when clicked
will toggle the display of some buttons for controlling the game
state.

This is not as clever as it could be. For example, only one of REVEAL
and START buttons need to be displayed at any given time, (depending
on the game state).

But this should work for everything the game host needs (other than
hiding players that have been captured).