Add map building script + docs

[TEAMJBMOD]

While we can't completely automate map compilation since you need to launch the game for proper cubemaps, we should have a standard .bat for vbsp + vvis + vrad, automatically add any packed files, and add the remaining instructions for cubemaps on the docs page

[TEAMJBMOD]

jb_buildingblocks zipped textures no longer working on Linux. As part of this we should add a presubmit that detects this, since I feel like this has happened before.