Collected user guide updates

[Matthias Clasen <matthias clasen gmail com>]

After my rant from last week, I felt that I should do something to
improve the situation.
The result of a few nights of doc updating is this list of patches
(most of them by me, some I found already sitting in bugzilla...).
Together, these address almost all the points I decried last week
(with the exception of the screen resolution capplet, which I haven't
tackled because I don't have working xrandr here atm):

• mouse preferences - bug 570923
• login photo - bug 570924
• window prefs - patch in bug 570915
• take screenshot - bug 571017
• keyboard shortcuts - bug 571018
• keyboard prefs - bug 571030
• assistive technology - bug 571134
• appearance capplet - bug 571140
• nautilus prefs - bug 571270
• nautilus - bug 571392
• sessions prefs - bug 502018
• preferred apps - bug 413452
• network settings - bug 571393

Getting these reviewed and committed before the string freeze would be
pretty awesome.

Matthias