Reset preferences on upgrade from incompatible version

* Resets all preferences on upgrade from a designated "incompatible
version" or older
* TrafficView falls back to default if preferences cannot load on
startup
Issues #31, #32, #35
Logger change to log non-null exception only
Fix problem with screen rotation and 'Network types' dialog

* Corrected problem with screen rotation and 'Network types' dialog (all
entries got populated, which is incorrect - types unsupported by device
must remain hidden)