Re-order global preferences -> display.

Put folder list options between account list options and message list
options, so the order matches the order the respective activities appear
on screen.
Improve Account settings -> notifications layout.

It makes no sense to display ringtone and vibration as children, but not
doing that for the vibration pattern and length. As double indention is
not available, un-indent ringtone and vibration and indent the vibration
parameters instead.
Merge pull request #239 from maniac103/improve-pref-layout

Improve layout of preference screens