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This changes the organization of lock screen security settings
to make choosing an alternate unlock method more discoverable.

Instead of having to disable the old lock method to use a new
one, the user now just has one set/change option in lock settings,
with a list of method-specific setting below it.

In addition, we ask the user to confirm their old credentials
before prompting them to choose a new one, which eliminates one
source of confusion.

Also, ChooseLockGeneric now shows a UI if quality isn't specified.
Any unlock method less secure than minimum specified by
DevicePolicyManager (if active) is greyed out.

Change-Id: Iecc6f64d4d3368a583f06f8d5fe9655cc3d5bd3b