per game settings

first draft, there's still some things I'm unsure about and this definitely needs testing (I barely tested any of the options and just acted like if one works, all work).

obvious points of discussion:

* which settings should be per game
* try to load game config in both "EmuScreen::bootGame" and "Load_PSP_ISO" ?
* what to do to not use `NativeMessageReceived("stop","");` but also unload the config with the windows menu via "Emulation->stop"

if all points of contention are cleared I'll squash this into one commit

~~**edit:** really confusing for users, when they long press (or right click) on a game and select game settings it will just modify the global setting like it always used to do, we need to either remove the "change settings" entry there or make it modify the per-game settings if it has some~~

**edit2:** now "Game Settings" does not appear in the "GameScreen" unless there is a game specific settings file and the pause screen calls it "Settings" when it's modifying the global settings and "Game Settings" when modifying the game-only settings
Hmm, this is definitely not the only place you can quit a game.  Won't bad things happen if unloadGameConfig isn't called?

What if I use the Windows UI to load a new game, or simply drag a new game into the window?

I think it'd be better for it to unload in like System.cpp or something...

-[Unknown]