settings: Make mobile settings a first-class citizen

* Nobody likes carriers, but let's not bury these settings behind
10 layers of indirection. Many users (like me) who travel often
will need to access these options frequently.
* The top level switch disables mobile data.

Change-Id: I1bd4d1116a2c73832230d66c94df2c3c0aacf698
cyanogen authored on Apr 14