Add module support & query their information during update cycle (#243)

* Add module support & modularize existing query

This creates a base to expose more features on the supported devices.
At the moment, the most visible change is that each update cycle gets information from all available modules:
* Basic system info
* Cloud (new)
* Countdown (new)
* Antitheft (new)
* Schedule (new)
* Time (existing, implements the time/timezone handling)
* Emeter (existing, partially separated from smartdevice)

* Fix imports

* Fix linting

* Use device host instead of alias in module repr

* Add property to list available modules, print them in cli state report

* usage: fix the get_realtime query

* separate usage from schedule to avoid multi-inheritance

* Fix module querying

* Add is_supported property to modules

kasa/modules/emeter.py

@@ -0,0 +1,20 @@
+"""Implementation of the emeter module."""
+from ..emeterstatus import EmeterStatus
+from .usage import Usage
+
+
+class Emeter(Usage):
+    """Emeter module."""
+
+    def query(self):
+        """Prepare query for emeter data."""
+        return self._device._create_emeter_request()
+
+    @property  # type: ignore
+    def realtime(self) -> EmeterStatus:
+        """Return current energy readings."""
+        return EmeterStatus(self.data["get_realtime"])
+
+    async def erase_stats(self):
+        """Erase all stats."""
+        return await self.call("erase_emeter_stat")