AF: Show passwords settings for available autofill service.

Separates autofill preferences into 2 categories - one for the passwords
settings and one for the existing default service preference.

The passwords preference controller dynamically creates preferences for
each autofill service.

Bug: 169455298
Test: manual
Test: TODO new test for controller
Change-Id: I369b5db00be75957c869df4d960595e9e1d9772c