Bug: 21589105 Rescoping SYSTEM_ALERT_WINDOW and WRITE_SETTINGS permission to an

explicit toggle to be enabled through Settings via Apps -> Advanced Apps.

Added new and refactored an old xml to define the UX for two new Preferences
in Advanced Settings. Modified the existing AdvancedAppSettings to add
control flow for two new settings. Also enriched ManageApplications to
handle these cases. Added additional strings in xml/values/strings.xml
to support these settings. Also defined new classes to handle these the
toggle of these permissions per app.

Refactored codes from AppStateUsageBridge to a generic AppStateAppOpsBridge so
that future usages related to AppOps can inherit from this class.

Change-Id: I43b81282a063e05844c7805556a6d05cfc02bcdb