context aware keybindings

[awb99]

Whenever you have an application that gets bigger, the global nature of keybindings gets more
and more complicated. I think what would be very cool is to have keybindings, that get active / deactive
with a context.

So say inside a text editor I want to use ctrl-s to save the document.
But on the main nav I want to have ctrl-s to open a settings dialog.
Or outside a text editor all keybindings related to editing should be gone.

Context could me an atom containing a key. And then keybindings could have
a new optional parameter context.