Changes w_class of mech parts. Fixes/adds descriptions.

For some reason mech parts all had a w_class of 20, which made their size show up as blank when examined. Changes to 6 so that they show up as "gigantic". Almost functionally the same, they won't fit in any bag.

Also adds and changes a bunch of descriptions to buildable mech parts, and renames a few to imply their use on mechs. Particularly "syringe gun" to "exosuit syringe gun".