New: F3 PreMount component

Function is named preMount and called by using [array] call f_fnc_preMount or [array,boolean,boolean] call f_fnc_preMount.

Parameters:
1. array containing vehicles & members of group to mount (1 per group is enough)
2. boolean to control whether non-cargo seats should be manned. Default is true.
3. boolean to control whether fireteam cohesion should be ignored (fireteams are split between vehicles). Default is false.