Add tests

[martin-t]

• shoot all weaps, make sure they don't hit owner but do hit enemy
• make sure bullets don't pass through vehicles when moving fast
  • also when vehicle moving in opposite direction (bullet trace could stop in from one frame, continue behind moved vehicle next frame)
• self destruct - proper delay, dead after
• GM - stop guiding and camera tracking on player death / impact / launching next
• z-order of explosions - SD, mines, weapons vs vehicle
• see notes in systems::input() about input going to the wrong entities