Add a powerswitch interface

libnymea/interfaces/interfaces.qrc

@@ -68,6 +68,7 @@
         <file>navigationpad.json</file>
         <file>extendednavigationpad.json</file>
         <file>closablesensor.json</file>
+        <file>powerswitch.json</file>
     </qresource>
     <qresource prefix="/"/>
 </RCC>

libnymea/interfaces/powerswitch.json

@@ -0,0 +1,10 @@
+{
+    "extends": "button",
+    "description": "The powerswitch interface is used for smart power switches and just extends the simple button interface. Use this for switches that can be on or off.",
+    "states": [
+        {
+            "name": "power",
+            "type": "bool"
+        }
+    ]
+}