Allow apps with SCORE_NETWORKS to set the active scorer.

This allows for a more streamlined UX in the current world, where
scorer apps are trusted (by virtue of being in /system/priv-app).
Trusted apps can continue to use the system dialog for consent, but
they may also set the scorer directly, under the assumption that they
are using their own consent UX to explain the feature to the user.

Bug: 16577529
Change-Id: I2a6edb7f1f688aaacf9b0152fa1da1a88636c3dc