Add several camouflage stages

[klemmchr]

Add different stages for camouflaging trenches. Could end up that trenches are fully covered by bushes.

[anfo55]

Nice idea. When I was in my country's army reserve, we learned of different pit (trench) stages:

1. Shell scrape. Shallow ditch that your body would lie in,
2. Stage 1 pit, perhaps what ACE/Grad trenches could be, about 500mm deep,
3. Stage 2 pit, deeper pit, sleeping bays added, not applicable to mod maybe,
4. Stage 3 pit, more or less fully developed, covered by OHC (overhead concealment) with extra camo as @chris579 mentioned

[AdlerSalbei]

In mod