Add _unload functionality

main.py

@@ -11,6 +11,18 @@ class Plugin:
     # Asyncio-compatible long-running code, executed in a task when the plugin is loaded
     async def _main(self):
         # startup
+        print("PowerTools starting...")
         self.backend_proc = subprocess.Popen([PARENT_DIR + "/bin/backend"])
         while True:
             await asyncio.sleep(1)
+
+    async def _unload(self):
+        # shutdown
+        print("PowerTools unloading...")
+        if self.backend_proc is not None:
+            self.backend_proc.terminate()
+            try:
+                self.backend_proc.wait(timeout=5) # 5 seconds timeout
+            except subprocess.TimeoutExpired:
+                self.backend_proc.kill()
+            self.backend_proc = None