Gun-tightening, pass 1

RM rifles, having burst capacity, are Assault weapons at best.  Same
with the Saiga.  Gave drug dealers the short-shotgun as it'd work quite
well in that capacity, IMO.  Still WIP.
LMOE grouping

Creates a specific group for guns a survivalist/gun-fan might have,
rather than the catchall "all_guns"; however, these guns come loaded.

Also cleans up a few descriptions in ranged.json and makes the Rivtech
civilian-market gear marginally more likely to show up in a
store-defense role (behind the counter).
Instates the homegun-basements and PD armory

This tightens and implements the new spawngroups.  Basically, civilians
go with rifles and shotguns rather than SMGs, and the police have far
less variety in the guns left around at base.

Cops can still have tonfas, grenade launchers, etc--just on their rezzed
person.  (And yes, some departments are procuring P90s IRL.)
comma fix
Add the DEEP_WATER flag.
Use DEEP_WATER flag for blocking vehicle water spawns.
Don't let marloss wipe out deep water.
Handle water properly when knocking creatures back.
Use DEEP_WATER flag for vehicle sinking.
Remove now-superfluous has_flag("LIQUID") checks,
Remove now-unnecessary SWIMMABLE flag check from quantum tunneling.
Use DEEP_WATER flag for diving into water.
Remove another now-unneeded SWIMMABLE flag check.
Use the DEEP_WATER flag when using > and < to dive/surface.
After handling water, don't then treat it like ground.
Use DEEP_WATER flag when displacing water.
Pruning more now-unneeded flags.
Use DEEP_WATER flag for is_divable.
Use DEEP_WATER flag when checking for underwater items.

Also, braces.
DEEP_WATER flag in can_move_to.