Add categories to Settings

- Screenshots: https://screenshot.googleplex.com/M0THHitYLg6.png
- Use PreferenceCategory to show section title.
- When removing a preference programmatically, we need to remove it from
  the PreferenceCategory it belongs to, rather than from
  getPreferenceScreen().
- Also add category and title for "contacts metadata".
- Delete string "Manage accounts" that was not removed in ag/938570
- This CL doesn't affect Dialer.

Bug 27687799

Change-Id: Ifa664f6ba50b784e4d90ef87aef3f3e35e27b209