One player can block the whole server forever

[bretonium]

Steps to reproduce:

1. Join the server, switch map to normandie
2. Start survival
3. Hide somewhere, where the bots cannot reach
4. Do nothing

Observed: the player can sit there forever, effectively blocking the game for everyone, because the bots cannot reach there. There is no way to remove them, because spectators cannot vote to kick other players. This leads to people joining the server, watching the game for a minute and then leaving in disgust.

Proposed: end survival if in 15 seconds no zombie was killed.

[bretonium]

Alternative: add new joining players to the game. Spawn them near one of the humans. This will also solve the problem, when users join and have to wait for the already running surival to end