Added logic_stripweapons entity

Specific entity to remove a weapon that targets a player activator
holds:

--keys--
keepfists: If yes, the stripallweapons input strips all weapons but
fists

--Inputs--
stripweapon: Strips a single weapon as mentioned in arguments
stripallweapons: Strips all weapons the activator has
setkeepfists: If 1 the stripallweapons inputs strip all weapons but
fists
enabled use of weapon_map_base in default ZS

Prevented weapon_map_base from being deleted so that people could use it
as a tool for creating map made custom weapons in non-ze game types.
Various additions to FGD

+ Added logic_stripweapons
+ Added weapon_map_base
+ Gave prop_nail "angles" keyvalue