[Request] Use menu bar instead of dock icon

[colejd]

This is a personal preference, so feel free to decline, but it feels to me like this is the kind of app that typically has a menu bar icon rather than an icon that lives in the dock. If you add momentary/toggle functionality from #23, you could also use the icon to show whether Keyb is currently in "flipped" mode or not.

[ZevEisenberg]

I thought I had an issue open for this, but I guess not. Thanks! I agree it would be useful; I just didn't think it was worth the effort to get it going for the first App Store release. It sounds like there's some fiddly stuff in terms of a background process and other machinery to get it up and running.

Not sure I'd want the icon to show whether it's in flipped mode, since that happens every time you hold the spacebar. Maybe just show whether it's enabled or not.