Populate military sites

* Add BLOL_fnc_ambiance_militarySites.
Set player as neutral captive in debug mode
Remove debug mode special cases for ambient combat and paradrops
Return captive units from BLOL_fnc_players_all
Clean up empty groups during GC sweeps
Simplify ambient military sites

* Fill military buildings around each site with highly-skilled OPFOR
units.
* Add BLOL_fnc_ambiance_populateMilitaryStructures.