Generalize smartdevice child support (#775)

* Initialize children's modules (and features) using the child component negotiation results
* Set device_type based on the device response
* Print out child features in cli 'state'
* Add --child option to cli 'command' to allow targeting child devices
* Guard "generic" features like rssi, ssid, etc. only to devices which have this information

Note, we do not currently perform queries on child modules so some data may not be available. At the moment, a stop-gap solution to use parent's data is used but this is not always correct; even if the device shares the same clock and cloud connectivity, it may have its own firmware updates.

kasa/smart/modules/childdevicemodule.py

@@ -1,4 +1,6 @@
 """Implementation for child devices."""
+from typing import Dict
+
 from ..smartmodule import SmartModule
 
 
@@ -6,4 +8,12 @@ class ChildDeviceModule(SmartModule):
     """Implementation for child devices."""
 
     REQUIRED_COMPONENT = "child_device"
-    QUERY_GETTER_NAME = "get_child_device_list"
+
+    def query(self) -> Dict:
+        """Query to execute during the update cycle."""
+        # TODO: There is no need to fetch the component list every time,
+        #  so this should be optimized only for the init.
+        return {
+            "get_child_device_list": None,
+            "get_child_device_component_list": None,
+        }