Prep work for GE and CPU on separate threads

So far I've got it working and drawing stuff, but it's got glitches (still need to fix some threadsafety issues), and I have a deadlock problem between the two threads that I'm still trying to debug...

Anyway, it'll need these changes.  They don't seem to break 3rd Birthday or FF Type-0 (before, using a threadsafe event did), so I think it'd be good to test these out first more widely.

I'm also not totally happy with it right now.  I'm using an event system and have things like InitClear and InitClearInternal.  The trouble is, I want the list management on the CPU thread of course, but I need all the GL calls on the GPU thread (EmuThread.)  I'm also worried this will be different for different backends (DirectX, Software, etc.)

-[Unknown]