Respawning server-side

I implemented respawning on the server-side. The client still needs a button to do this.

Currently respawning fills your HP and sends you back to the starting location. A mechanic for saving a different spawn location will be needed, but this will be postponed to Milestone 9.

I also implemented the /death and /revive chat commands.

Something which is also a bit annoying is that there is no way to tell if a player is alive or dead just by looking at them. I need to use a different sprite for dead players.