Convert ammotype from an enum to a std::string to allow more values.
Change ammo type identifiers to lower case.
Fiddled with the popup message for when an NPC gives the player something to avert a segfault.
Merge PR#2058 - Fix NPC item give crash
Merge PR#1998 - Ammotype to std::string

Conflicts:
	data/raw/items/ammo.json
	veh_interact.cpp
	vehicle.cpp