[ui] Node: Added property denoting if the node delegate is a backdrop

Author: waaake

meshroom/ui/qml/GraphEditor/Node.qml

@@ -19,6 +19,7 @@ Item {
     property bool readOnly: node.locked
     /// Whether the node is in compatibility mode
     readonly property bool isCompatibilityNode: node ? node.hasOwnProperty("compatibilityIssue") : false
+    readonly property bool isBackdrop: false
     /// Mouse related states
     property bool mainSelected: false
     property bool selected: false