Only return active ConsumptionTypes in API

piket_server/__init__.py

 @app.route("/consumption_types", methods=["GET"])
 def get_consumption_types():
     """ Return a list of currently active consumption types. """
-    ctypes = ConsumptionType.query.all()
+    ctypes = ConsumptionType.query.all().filter_by(active=True)
     result = [ct.as_dict for ct in ctypes]
     return jsonify(consumption_types=result)