[BluetoothLEExplorer] fix warnings

Xamarin.iOS 8.6.0.12
[BluetoothLEExplorer] drop this

Xamarin.iOS 8.6.0.12
[BluetoothLEExplorer] simplified namespaces

Xamarin.iOS 8.6.0.12
[BluetoothLEExplorer] simplified ScanButton

Xamarin.iOS 8.6.0.12
[BluetoothLEExplorer] factor the code. move classes to separate files. drop "_" prefix

Xamarin.iOS 8.6.0.12