Clean up some VRAD command descriptions, and add `-nodrawtriggers` to VBSP

[SirYodaJedi]

Synopsis:

• $alphatest works for texture shadows, not just $translucent (thank goodness)
• -smooth is for brush faces that don't have a smoothing group (that's why there are flat shading groups)
• -extrasky 16 is implied by -final (so you probably don't need it)
• lights files are sometimes called RAD files, because of the file extension (I recently made a VDC page for them)
• -staticproplightingfinal is now implied by -final
• -nodrawtriggers can be used to shrink BSP file size a miniscule amount (it's probably useful to someone making humongous gmod maps)