Fixed melee spawns and IED damage to defences

Doubled all defence part hitpoints, made TNT explosives do two hitpoints
of damage and IEDs do one.

Renamed "Explosives" to "TNT" due to the addition of IEDs, technically
they are BOTH "explosives" so this new name will make distinguishing
between them easier.

Fixed a bug with melee weapons, if the extradata (ammo) was set to 0
(which happens a lot in loot spawning) melee items wouldn't become
weapons when picked up.

Fixed some other bugs including a possible line of code that was
blocking the give action for all items apart from weapons (untested at
this time)