Add region management

This adds region management: the user can manage a list of available regions
and for each channel pick a region from that list to apply to messages.

Region discovery from nearby repeaters will be done in a separate PR.

This is a part of the work needed for #120.

lib/services/ble_debug_log_service.dart

@@ -176,6 +176,8 @@ class BleDebugLogService extends ChangeNotifier {
         return 'CMD_SET_CUSTOM_VAR';
       case cmdSendTracePath:
         return 'CMD_SEND_TRACE_PATH';
+      case cmdSetFloodScope:
+        return 'CMD_SET_FLOOD_SCOPE';
       default:
         return null;
     }