There are three main thrusts of this pull request:
Implement a pairing database, and pairing UI. The device goes into advertising mode when you enter the settings menu (which is created in this PR), and only accepts new pairing requests at that time. Pairing is not quite implemented the way real Pebble devices do it, but this appears to be compatible with the Pebble app.
Shore up the PPoGATT (and, while we're at it, everything else Bluetooth) support, especially on nRF52. This allows nRF52 to reliably talk to the Pebble app, whenever the Pebble app can be bothered to establish a connection, anyway.
Fix a few protocol-layer things, but not much. The watch still can't, for instance, convince the Pebble app to send it an app list, and the watch doesn't have a way of recording what it was most recently connected to, so it can't mark itself as "faithful" or "unfaithful" to the phone (and avoid the full-database-wipe that is mandated in such an event).
There are three main thrusts of this pull request: