Settings: Add Superuser entry

Squashed commit of the following:

Author: Koushik Dutta <koushd@gmail.com>
Switch to new Superuser
Change-Id: I9d91392ad6fbc9953d19059ab59b91d214c00e0c

Author: Danny Baumann <dannybaumann@web.de>
Hide Superuser entry if root access for apps is disabled.
Change-Id: Ibb77ba5a0fccf22564a26b8b1e13f7762c65718e

Author: Ricardo Cerqueira <cyanogenmod@cerqueira.org>
Development: Root for apps is unavailable if the su daemon isn't running

The superuser options are tied to the Superuser app variant we use,
which in turn is tied to the su daemon. No daemon, no menu options.
Change-Id: I41d58e62986759336ab38e67f26a558c2eed5aa3

Change-Id: I9d91392ad6fbc9953d19059ab59b91d214c00e0c