Implement client-side pairing

[bherbst]

Sorry, this ended being a little bigger than expected.

This PR adds the client side bluetooth connection logic.

• Adds button on the server screen to connect a new client - required to make the server discoverable to new clients
• For API 26+, implements pairing via CompanionDeviceManager, which doesn't require location permissions
• For < API 26, implements pairing via traditional bluetooth scanning APIs, which does require location permissions on some API levels
• Updates scouting home screen to support finding a server

Next up: actually sending/receiving data over bluetooth