Final platform settings UX for ephemeral networks.

Show "Connected via Wi-Fi assistant" instead of just "Connected" when
a Wi-Fi connection is ephemeral. Otherwise, treat ephemeral
connections just like saved ones - show (read-only) connection stats
when you click the network, and offer the ability to "forget" the
network, which prevents further ephemeral connections.

Bug: 18525241
Change-Id: I0d2146ab47b82d32c50b2ef883f176a6b6066713