[ui] Graph: Added support for Node deletion with Backspace Key

In standard MacOS keyboards the backspace key is referred to as the delete key. Supporting both backspace and delete keys for delete operation in the graph ensures consistency across the different key layouts across devices.

Author: waaake

meshroom/ui/qml/GraphEditor/GraphEditor.qml

@@ -139,7 +139,7 @@ Item {
     Keys.onPressed: {
         if (event.key === Qt.Key_F) {
             fit()
-        } else if (event.key === Qt.Key_Delete) {
+        } else if (event.key === Qt.Key_Delete || event.key === Qt.Key_Backspace) { // Backspace supports both Windows and MacOS Keyboards
             if (event.modifiers === Qt.AltModifier) {
                 uigraph.removeNodesFrom(uigraph.selectedNodes)
             } else {