Fix singleplayer cutscenes.

[DreamyCecil]

The synchronization is still bad. The actions and current camera should probably be implemented in a global entity and then pulled from it by players.

• All players but the first one should be teleported away from the world during any actions with the camera on (and teleported back to the first player when no active camera).
• All players should be in the same spot each time PlayerActionMarker sequence is finished.
• All players should have the same weapons by the end of the sequence if any new weapons have been received in a cutscene despite the shared weapons option.

[DreamyCecil]

Seems like all is done now (God, I hope so).

• The player that triggered the cutscene will be the one visible in it (cutscene actor).
• Any PlayerActionMarker that affects player position in any way is used for teleporting other players after the sequence is finished.
• Collected weapons are distributed to all players and not just the actor that collected them.

[DreamyCecil]

Nope, seems like there are still critical bugs. Players keep overflowing the stack by entering infinite cycles of PlayerActionMarkers on some maps.

[DreamyCecil]

Latest commit seems to have fixed everything again. Will reopen it again once new issues arise. Hopefully not.