add firmware property + convert device list to dict (#719)

* add firmware property

* convert devices list to dict

miio/gateway.py

@@ -126,7 +126,7 @@ def __init__(
         self._radio = GatewayRadio(parent=self)
         self._zigbee = GatewayZigbee(parent=self)
         self._light = GatewayLight(parent=self)
-        self._devices = []
+        self._devices = {}
 
     @property
     def alarm(self) -> "GatewayAlarm":
@@ -151,7 +151,7 @@ def light(self) -> "GatewayLight":
 
     @property
     def devices(self):
-        """Return a list of the already discovered devices."""
+        """Return a dict of the already discovered devices."""
         return self._devices
 
     @command()
@@ -172,7 +172,7 @@ def discover_devices(self):
             DeviceType.AqaraWallOutlet: AqaraWallOutlet,
         }
         devices_raw = self.get_prop("device_list")
-        self._devices = []
+        self._devices = {}
 
         for x in range(0, len(devices_raw), 5):
             # Extract discovered information
@@ -203,7 +203,7 @@ def discover_devices(self):
 
             # Initialize and save the subdevice, ignoring the gateway itself
             if device_type != DeviceType.Gateway:
-                self._devices.append(subdevice_cls(self, dev_info))
+                self._devices[dev_info.sid] = subdevice_cls(self, dev_info)
 
         return self._devices
 
@@ -639,6 +639,11 @@ def device_type(self):
         """Return the device type name."""
         return self.type.name
 
+    @property
+    def firmware_version(self):
+        """Return the firmware version."""
+        return self._fw_ver
+
     @property
     def battery(self):
         """Return the battery level."""