Let players win rounds

[thecoshman]

depends on #27

Server

• once a players score reaches a certain value (13 to start with, because don't question me) end the round, reset all scores, respawn all players, send a 'round over' message to clients and then a full world start message

Client

• on receiving a 'round over' message, display this to the player, stop sending updates until the next full world start message is sent

Misc

No need for a formal 'round start' message, the first full state update message can signify that for now.
The exact format of the 'round over' message can be defined later.