Offline

Change-Id: I6371df8e092905e2585dfd30ffa93cdf491e4f6f

Added support for searching bssids in an offline database. Just like @n76 Local-GSM-Backend.
I integrated it into your backend because it kinda makes sense ;)
If you want me too, I can also publish this as my own backend.
:+1: Once you add the meta-data BACKEND_SETTINGS_ACTIVITY (as you did) and mark the activity as exported using `android:exported="true"` (which you missed out) it will show up in the UnifiedNlp settings in the overflow menu next to the backend. There is no reason to show a feature in the launcher, the user merely uses.