Redesign settings for tablets

1. Move AppCompatPreferenceActivity from Dialer to ContactsCommon
2. Move ContactsPreferenceActivity from Contacts to ContactsCommon,
   make it extend AppCompatPreferenceActivity and avoid building
   headers (by not overriding onBuildHeaders)
3. Move the "About" PreferenceScreen to preference_about.xml and
   add AboutPreferenceFragment so that we could switch between two
   fragments.
2. Add "back button" to LicenseActivity.

Here's how it looks:
https://docs.google.com/a/google.com/presentation/d/1A5n2o8epBCrizZvbOyelvjoHz-s5-IRlJd-KqWAMBao/edit?usp=sharing

Bug: 25629359
Bug: 26469731
Change-Id: If88722a62e41d1a2f4f70939b2d52d697e204628