Add round results concept

[t3kt]

When a round ends, there should be a set of information available that indicates:

• what caused the round to end (time limit, all bricks destroyed, all balls destroyed, all players killed, all players disconnected, etc)
• score for each player
• how long the round was
• bricks destroyed vs total bricks
• balls destroyed vs total balls
• powerups acquired

This information should be available in the round ended event, and will be used to:

• display a message in the dome space
• send out some sort of message to the players (if they're still connected)

see also #19