Add activity for mobile network page

1. Extract the Tabhost to activity level, not fragment level. So
each mobile fragment has a constant subscriptionId
2. Use BottomNavigationView instead of TabHost

Bug: 114749736
Test: RunSettingsRoboTests
Change-Id: I43aebf2ec01a945697c6b2302ab750e715e4bfef
7 files changed