Respawn

Basic respawning implemented. Currently, people only respawn in one place, independent of everything. We eventually probably want the map to determine the spawn positions, and have a variety of different spawns for each team.

I'm sending this pull request now because I probably won't get a chance to work on this for a bit, and this implements enough functionality that all of the shooting/health work which has been done might perhaps finally be able to merge into master.