Multi-user - 1st major checkin

Switching activity stacks
Cache ContentProvider per user
Long-press power to switch users (on phone)

Added ServiceMap for separating services by user
Launch PendingIntents on the correct user's uid
Fix task switching from Recents list
AppWidgetService is mostly working.

Commands added to pm and am to allow creating and switching profiles.

Change-Id: I15810e8cfbe50a04bd3323a7ef5a8ff4230870ed