Bluetooth pairing UI

[jwise]

Pairing is a big one! 🍐

• [x] Bluetooth pairing request/response/status API design from Bluetooth stack into OS.
• [x] Bluetooth pairing connection parameter storage API design from Bluetooth stack into OS.
• [x] Bluetooth pairing connection parameter storage on filesystem (see #71).
• [ ] Menus for Bluetooth configuration and management.
• [x] UI for pairing request.

[jwise]

ac9e91f does some proof of concept pairing response.