Work on issue #21589105: Scope WRITE_SETTINGS and SYSTEM_ALERT_WINDOW...

...to an explicit toggle to enable in Settings

Add a new permission flag, saying the permission can be automatically
granted to pre-api-23 apps.  Apply this to SYSTEM_ALERT_WINDOW.

Change-Id: I24a0ceabe7e9f5e458a864d30eda2696ad14a699
8 files changed