Change the way ON key combos work

[ddevault]

Right now, when you press ON, the kernel will check the pressed keys during the interrupt handler. This is lame for several reasons:

• Fucks up the keyboard state back in userland if we interrupted a keyboard operation
• Requires you to press the other bit of the key combo first, which sends a key input to the running program

Alternative idea: press ON, followed by a key. The kernel will stop userland from getting key inputs until you do, and then resume. This gets the keyboard code out of the interrupt, and means you can do meta actions without sending a key to the running program. We can also extend this to userspace, letting them register meta key handlers.