UIFe: Update keyboard shortcut overlay with more consistent wording

[Jeremy Bicha]

Hi, Unity 3D's new keyboard shortcut overlay (when you press and hold
the Super/Windows key) has rather inconsistent grammar and wording.
I've submitted a branch proposal to improve this.

https://bugs.launchpad.net/ubuntu-translations/+bug/964673

I apologize for the late notice and I realize this changes several
strings. Is this something that can happen for Precise?

Thanks,
Jeremy Bicha