Shoretrooper Backpack Full Fix (Sean Fields)

This is a Sean Feilds provided Shoretrooper file backpack fix to Level 2 specs.

Fixes,
- Vents (Done by derekp14)
- Top Right Disk Recess added
- 2 Gribblies added above the backbox frame on each side
- 3 cutouts added to left backpack
- 1 lower cutout added to right backpack
*will need to add a circle gribbly yourself in lower center once both pieces are pieced together for level 2 legion approval review, please see CRL on 501st page