People: Action bar tab refactoring

- Now ActionBarAdapter manages the action bar tabs.
- Now ActionBarAdapter.setCurrentTab() should always be used to select
  a tab programmatically, rather than directly calling
  ActionBar.setSelectedNavigationItem().

- Do not re-create/re-initialize ActionBarAdapter/ActionBar for new
  intents.

- Simplify fragment visibility update logic in PeopleActivity.

- Do not clear ActionBarAdapter.Listener in PeopleActivity.onPause;
  do this only in onDestroy.
  Activity is paused when we're processing onNewIntent(), but we still want to
  get callbacks during this.

Change-Id: I93ec35e569e1854923503734693b6404cff92f50
3 files changed