DevicePolicyManager per user

Bug: 7136483

Store device policy information for each user and apply them when user switches.

Global proxy can only be controlled by owner.
Camera restriction applies to all users, if any one has an admin that disables it.
Storage encryption can only be controlled by owner, although other users can query the state.
Wipe data will only remove the user if non-zero, wipe the device, if zero.

Change-Id: I359be46c1bc3828fd13d4be3228f11495081c8f2