Fix one source of config disconnect problem

The MainActivity is using a fragment stack on a container for About and
Config but a different stack on a different container for
NearbyDevices. The result is a missing onPause call when entering
BeaconConfigFragment. This kept the BLE scan running at LOW_LATENCY.
Scanning and GATT connections cannot occur at the same time so this was
causing a problem.
Merge pull request #70 from schilit/Config-Bug

Fix one source of config disconnect problem.
Good find, thanks! Merging!