Gm_EarthDig2 addon

The second version of the original Gm_EarthDig map.
The official release thread is In the mapping releases forum of FacePunch Studios.

This is a multi-layer breakfloor map. It has 896 breakable blocks, each layer with different health. The layers are going pretty realistically (sadly just the order), first grass, then dirt, and at the end, hard rock.

New stuff:
- 3D skybox (I know it's still not very smooth, but I want to reduce the load as much as possible)
- Minor stuffs
- Admin room (accessible only with noclip) with:
- - Separate block respawn button
- - Ability to enable/disable the public block respawn button (at the spawn)
- - Ability to delete or restore seperate layers

Stuff not changed:
- Layer texturing
- Number of blocks (the max_map_models is already at 88%)
- Block health
- Respawn layer by layer

I know that:
- 3d skybox ground and map ground don't align 100%. That is because you can only have 2 decimals in texture alignment (0.01) instead of as much as I would need (0.0125)
- There is still the same number of blocks
- There are no blocks spawned at start. Just click the button and wait 15 seconds.