Mouse preferences docs update

[Matthias Clasen <matthias clasen gmail com>]

I've put a patch in http://bugzilla.gnome.org/show_bug.cgi?id=570923
that brings the documentation for the mouse capplet in line with the
current ui. The information for the a11y tab was largely taken from
http://live.gnome.org//Mousetweaks/Home?action=show&redirect=Mousetweaks
It would probably be good to get some feedback from the mousetweaks authors.

Please review and apply.


Matthias