Layer user restrictions

- Now DPMS remembers user restrictions set by DO / PO in their ActiveAdmin.

- User restrictions set by DO/PO will no longer be saved by UserManger.  Instead,
when needed, UMS will consult DPMS to build "effective" user restrictions.

- UM.getUserRestrictions() will now always return "effective" user restrictions.

- DPMS migrates existing user restrictions per the eng spec.

- Also now UM.setUserRestrictions() will crash.  UMS.setUserRestrictions() has
been removed.
This was needed because UM.setUserRestrctions(UM.getUserRestrictions()) will no
longer be a valid use like it used to be.

- Also introduced a fined-grained lock for user restrictions in UM to avoid
deadlock between DPMS and also for better performance.

Bug 23902097

Change-Id: If0e1e49344e2f3e9226532d00777976d1eaa7df3