Added 'sabotage' ability for saboteur

"Sabotage" ability:
- unit is always cloaked and can only be seen by marines
- unit 'attack' vs capturable: capture without damaging
- unit 'attack' vs uncapturable: damage to 1hp
- all attacks are suicide attacks
- can't sabotage vs castle
Various bugfixes

- Saboteur can no longer sabotage castle
- MPGameClient no longer tries to reconnect when the game ends
- GameServer correctly resets reconnect flags so that more than one game can be played