Fix #74

- This mainly fixes issue #74 - we now make sure that a temporary scan stop can not become permanent, regardless of what happens, by simply making sure we resume after a timeout. This problem could occur, for example, when the other device’s BT crashed and we neither received a connect or connectFailed callback
- the lost connections timer is now only started when not running already, previously it was restarted in that case
- minor changes to CWBluetoothConnection states
- minor code cleanups