* set description before creating content to use the automatic
preference page header
* remove all unneeded margins and spacing
* center align icon and warning text
* remove fixed line break from header

The only remaining issue is the use of fixed line breaks in the warning
text label.

Change-Id: I02d65fcb272aac223d75ad6203aade5829799183
Signed-off-by: Michael Keppler <Michael.Keppler@gmx.de>
Bug:535979