New item - Improvised explosive

Adding a new creatable item, the Improvised explosive.

Recipe is Dr. Gibb Can + Igniter, Use assembly on a welding tank, then add wires. This creates a throwable grenade on a 5 second timer with a -1,0,2 sized explosion (Identical to a welding fuel tank explosion).

Works on Dr. Gibb cans only so there's a limit, but still easily accessible. Also, because Gibb, explosives, so fahnny joke

Tested it and haven't found any issues. If something looks atrocious, let me know!