Add Nextbit release signature to allow-permissions

This release signature has been used in all alpha builds and will
continue to be used by APKs published via the Google Play Store.

Change-Id: Iec9216dd02e4ca1ed77b0c97e1ef0bf2507348b7
permissions: Add screencast permissions

Screencast needs the following system permissions:
  android.permission.CAPTURE_VIDEO_OUTPUT
  android.permission.CAPTURE_SECURE_VIDEO_OUTPUT

Change-Id: I1e348ebe03dd25f0ef1b5476716beb73880547be