Fixed grenade casing not being renamed to grenade when complete

Fixed grenade casing not being renamed to grenade when complete and made
all assembly messages refer to the assembly as "grenade assembly".

- The grenade assembly is called "grenade casing" before anything is
done (like it always was)
- The grenade assembly is called "unsecured grenade" when a activation
mechanism is added (like before
https://github.com/tgstation/-tg-station/commit/f645037dd5ffe491c94f73a39b3aac312e51d579)
- The grenade assembly is called "grenade" when finished (like before
https://github.com/tgstation/-tg-station/commit/f645037dd5ffe491c94f73a39b3aac312e51d579)
- Renamed large chem grenade to "large grenade casing"
- Made using a wrench on a unsecured grenade remove the payload on the
first use, and the activation mechanism on the second use (because we
don't want to always remove both at the same time)
- Made cable_coil drop on the floor if it was used as activation
mechanism