Visual effects are applied to all screens

[andreasf]

When using multiple monitors, visual effects occur on all monitors, not only the "affected" monitor:

When on a secondary screen Q runs in fullscreen mode, Command+< results in spinning cubes on both screens. Instead, only the secondary screen should rotate in this case.

Same thing for fade-through-black for entering and leaving fullscreen mode.

[cordney]

Q uses the main screen for all transitions and fullscreen ([NSScreen mainScreen]). Problem is getting the current screen the Guest PC is being displayed on. Once this is possible, this can be fixed.