fix CBA_fnc_selectWeapon, add CBA_fnc_isPerson and CBA_fnc_canUseWeapon

[commy2]

fixes:

• CBA_fnc_selectWeapon doesn't work when the unit is in a firing from vehicles slot.
• CBA_fnc_selectWeapon doesn't work when the local player has not the same weapon as the unit.

adds:

• CBA_fnc_selectWeapon can now select vehicle weapons.
• CBA_fnc_selectWeapon has an optional paramter to select a specific weapon mode.
• CBA_fnc_isPerson which checks if an object is a person (soldier, civilian etc.).
• CBA_fnc_canUseWeapon which checks if a unit can currently use it's rifle, pistol or launcher. (Basically true on foot and in FFV slots, proved itself very usefull in ACE)