Network statistics display

[assertivist]

When there are networking issues during a game, the rendering completely stops and the game blocks until the missing frames are received from other clients.

At the very least, we should throw up some kind of visual indicator that the game is waiting on the network.

For bonus points, show the player list along with the most recent RTT and indicate which player is behind on frames.

For super extra bonus points, keep track of the RTT over the last N frames and show a graph on the indicator for each player with their RTT over time, with outlying maxima colored red. Decouple the network wait so that it doesn't block the rest of the application and rendering updates can proceed/chat input can be gathered.