Package restrictions per user

Packages can be enabled/disabled per user.
This requires maintaining stopped/launched states and
enabled / disabled components and packages per user.

Refactored pm.Settings and PackageSettingsBase to keep
track of states per user.

Migrated the stopped-packages.xml to users/<u>/package-restrictions.xml

Changed intent resolution to handle individual user restrictions.
Bunch of IPackageManager calls now have a userId argument.
Make AppWidgetService handle removals of packages.

Added some tests for pm.Settings and PackageManager.

Change-Id: Ia83b529e1df88dbcb3bd55ebfc952a6e9b20e861