[DONE] Added 'unmanned' UFO flag

[Meridian]

Unmanned UFOs (e.g. missiles, drones, etc.) cannot crash land after dogfight and cannot be forced to land by a tractor beam. They fight until 0% HP (not 50% HP).

Example:

Code: [Select]

ufos:
  - type: STR_SMALL_SCOUT
    unmanned: true