Add setAuto() method to change HomeState (presenceLock) to Auto

PyTado already has methods to set this to Home and Away,
but no method to set / revert it to Auto mode.
This change sends a DELETE request to presencelock, as does my.tado.com.

PyTado/interface.py

@@ -370,7 +370,7 @@ def setZoneOverlay(self, zone, overlayMode, setTemp=None, duration=None, deviceT
 
         data = self._apiCall(cmd, "PUT", post_data)
         return data
-        
+
     def getZoneOverlayDefault(self, zone):
         """Get current overlay default settings for zone."""
         cmd = 'zones/%i/defaultOverlay' % zone
@@ -390,7 +390,13 @@ def setAway(self):
         payload = { "homePresence": "AWAY" }
         data = self._apiCall(cmd, "PUT", payload)
         return data
-
+
+    def setAuto(self):
+        """Sets HomeState to AUTO """
+        cmd = 'presenceLock'
+        data = self._apiCall(cmd, "DELETE")
+        return data
+
     def getWindowState(self, zone):
         """Returns the state of the window for Zone zone"""
         data = self.getState(zone)['openWindow']