Sandbags overhaul

Vanilla sandbags changes:
- Each sandbag build costs 1x sandbag
- Each sandbag build returns 1x sandbag on dissasembly
- Added two more builds (screenshot, two of each bag type)
- MG nest build build/remove time 15s
- Dirt mount sandbag build/remove time 10s
- GMs can delete/move builds