Storing and using user id for pinned shelf apps.

We need this to differentiate between starting apps for the primary and
managed users.

This in particular solves the issue when apps were executed as Owner
while we are in Guest account (see the bug).

Valid user ids for a shelf app are either primary or a managed (work)
user for the profile.
Launcher allows mixing apps for for primary and the managed users on
its home screen. Apps for the managed user are marked with a suitcase
badge.

Launcher includes a user id in the drag and drop info that it sends to
SystemUI, as “profile” extra added to the intent.

Shelf now stores this user id and uses it to start apps.

Bug: 22609426
Change-Id: Id4c6c1ac8617a83f4484f78db578955699d1a888