Fix carrier and FARP spawns in multiplayer

[zhexu14]

This PR updates the population of warehouses to add the allowHotStart key and uses ints instead of strings as unit IDs. These changes affected multiplayer missions where units spawned on carriers / FARPs.

Without these changes, the following will generate a .miz file that works fine for single player but does not allow spawning in multiplayer.

from dcs.mission import Mission
from dcs.ships import Stennis, HarborTug
from dcs.planes import FA_18C_hornet
from dcs.helicopters import Mi_8MT
from dcs import countries  
from dcs import mapping
from dcs import unit


mission = Mission()
blue = mission.country("USA")
sg = mission.ship_group(blue, "Carrier", Stennis, mapping.Point(-200000, 450000, mission.terrain))
ag = mission.flight_group_from_unit(blue, "Player", FA_18C_hornet, sg)
ag.units[0].skill = unit.Skill.Client
mission.save("carrier_spawn.miz")