more bspzip options

[granis48]

Currently we have the PACK and REPACK processes that make use of bspzip for packing and compressing the bsp, but there is currently no option to decompress the bsp or use other bspzip features.

I don't know the best way to implement this other than adding a new process called BSPZIP that lets you use all of the programs parameters the way you'd like.
The question then becomes if PACK, or more reasonably REPACK, should be part of this new process instead of all three alongside eachother.

The specific features that prompted this issue is -repack (without -compress) to decompress BSPs, and -deletecubemaps which despite the name actually deletes all VTFs inside the BSP. These are both rather niche but do have their use cases.

https://developer.valvesoftware.com/wiki/BSPZIP