Fix lua errors for grey team barracks & base props

Spawn-menu icons for map entities, additive selection (holding shift to select more units) now works correctly.

Got rid of flamethrower spawn-offset

Fixed mammoth barracks not spawning mammoths.

More descriptive error if the tool file fails to load, some minor improvements.

Clientside performance improvements

Fixed (some) non-mw entities causing errors when spawned via the contraption system.

Fixed base-prop HP not getting set properly.

Fixed melon wars entities not spawning as parts of contraptions for non-admins.

Fixed contraption spawning lua-error on the 64 bit branch of gmod.