Add ability to switch to window in zone

[sid-6581]

This adds keyboard shortcuts to directly select a window in a zone. The default shortcuts I used is a bit clunky, I'm definitely open to suggestions for better ones.

Note that if the window in the selected zone is already active, it will cycle through the windows, same as switchToNextWindowInCurrentZone. That is on purpose, since that is the behavior I personally prefer, but I'm open to making that configurable if desired.

[sid-6581]

Oops, looks like it's not just activating the topmost window when selecting a zone, it's cycling immediately. I'll fix that.

[gerritdevriese]

Thanks for contributing. Tested and working as expected.

The current default shortcut doesn't seem to working for me though, I think shift overrides the numlock. My proposal is Meta+Ctrl+Num+1-9 (or you can also not pass the sequence key for no default)

If you want, could you also add the new shortcut to the readme file?

Cycling between windows after focus doesn't seem like a problem, it is actually quite intuitive.

[sid-6581]

I'm so sorry, I don't remember getting a notification about your reply. I'll definitely make those changes! I've got a couple of things to take care of first but I should be able to get to it over the weekend or early next week.