Adds vox spike thrower, makes crossbows and pneumatic cannons buildable on-station.

Merge #4941 before even looking at this one! I tacked it onto my drone branch due to some icon conflicts if I tried to do them with seperate forks of dev.

This adds a vox weapon, the spike thrower, which is a three-shot ammo-regenerating crossbow-like weapon. A naked human is hit for 30 brute by the spikes (during testing) and it takes several seconds for a shot to regenerate.

Crossbows can be built from wooden planks, cables, plastic sheeting and metal rods.

Pneumatic cannons can be built from metal sheeting, an atmos pipe, and a tank transfer valve.