events: Remove an unnecessary check
events: Move keybindings event handling out of the giant switch
events: Move the overlay_key_only_pressed handling to keybindings.c

Now the switch statement is entirely about window operations.
events: Remove extra check for certain grab op

We already explicitly test that there's no grab op right below.
events: Replace a switch statement with a simple if test
events: Swallow all events directly on windows

This is how the X11 mode works.
events: Clean up event replay code
events: Move window button handling to window.c

Look at how clean GCD is now!!!