BLE backend screens

BLE status and scanner screens that halps to create examples with ble_backend library

Usage

Just implement PeripheralScreen and use as follows:

ScannerScreen(
    bleCentral: bleCentral,
    bleScanner: bleCentral.createScanner(serviceIds: serviceIds),
    createStatusScreen: (bleCentral) =>
        StatusScreen(bleCentral: bleCentral),
    createPeripheralScreen: (blePeripheral) =>
        PeripheralScreen(blePeripheral: blePeripheral))