Update UI for Wifi Direct settings

- Change the launching preference from using an intent to directly a
fragemnt
- Partially convert WifiP2pSettings to a DashboardFragment
- Add a controller to control each pref category, when they have no
child, hide.
- Add a controller to control device's own AP name.

Change-Id: I23685c4d4a85f80ceab5a576005e693e6f8b7cc4
Fix: 36859626
Test: make RunSettingsRoboTests