VPNProfileList: Reinstate FAQ hint

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
VPNProfileList: Redraw "add profile" dialog on activity restart

Currently the code leaks the alert dialog on e.g. screen rotation events.
Fix this so that the alert's state is properly saved/restored, and the
alert is destroyed if it is active when the fragment is destroyed.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>