User management and switching

Broadcast intents that get sent out when users are added/removed/switched.

More work on generating user-specific information in package manager queries.
APIs to update user name and query a user by id.
Removed Package.mSetStopped and mSetEnabled, since they're not user specific.

User removal:
- Cleanup ActivityManager, PackageManager, WallpaperManager, AppWidgetService
  and AccountManager.
- Shutdown processes belonging to the user.

Don't show vibrate option in long-press power if there's no vibrator.

Lock the screen when switching users, to force unlocking.

Change-Id: Ib23a721cb75285eef5fd6ba8c7272462764038fa