Give botlib com_basegame for botlib.log path

Before it always used BASEGAME fallback code.
Don't scale shadow multipliers by overbrightbits, and improve documentation.
Merge remote-tracking branch 'ioquake3/master'
Remove BASEGAME fallback from botlib

basegame libvar is always set by engine.
Moved setting 3 bot lib vars from game to server

It should just be specific cvars, don't want game setting them to something else.