AppOps: track op persistence by name instead of id

On XML write, include the op name.  On XML read, map
the name back to op id (if it exists).

Persistent AppOp state now follows the op name instead
numeric id.  This allows upgrades between versions of
android that have different code<>name mappings.

Change-Id: Iffc02095b6838a34ff999f8db51c2c6739dd0db8