[DO NOT MERGE] Merge ContactsDrawerActivity and PeopleActivity (1/2)

- Created by cherry-picking Ia67586501836af6a8bef633c682480d94e2c1869
  and resolving conflicts so as to reduce merge conflict to master-dev.
- Downgraded visibility of many methods and variables to private.
- Rename mAllFragment as mContactsListFragment

Bug: 34066506

Test: quick sanity test

Change-Id: I13b20b078a42de50c69bee2b3abc97c72335c607