Changed ingame radio call signs.

A change to the briefing. As some players noted, I should have been talking about squads, not platoons. This is now fixed! :)

Added a new trigger to detect when there are 4 soldiers or less left in Charkia. Once that amount has been reached a countdown starts to the end of the mission. Hopefully this reduces the looking around for the last tango.

Fixed an error with callsign Archangel. It was waiting for a trigger that I had deleted and forgot to edit the helicopter's waypoint. Another update will follow soon to change the mission ending parameters a bit.