Import a scene from an .mg file into the current graph

Add an "Import Scene" (Ctrl+Shift+I) option in the File menu
that allows to select an existing .mg file and import it in the
current graph.

The imported scene will automatically be placed below the lowest
existing node along the Y axis.

meshroom/ui/qml/main.qml

@@ -304,6 +304,16 @@ ApplicationWindow {
         }
     }
 
+    FileDialog {
+        id: importSceneDialog
+        title: "Import Scene"
+        selectMultiple: false
+        nameFilters: ["Meshroom Graphs (*.mg)"]
+        onAccepted: {
+            graphEditor.uigraph.importScene(importSceneDialog.fileUrl)
+        }
+    }
+
     AboutDialog {
         id: aboutDialog
     }
@@ -530,6 +540,12 @@ ApplicationWindow {
                     }
                 }
             }
+            Action {
+                id: importSceneAction
+                text: "Import Scene"
+                shortcut: "Ctrl+Shift+I"
+                onTriggered: importSceneDialog.open()
+            }
             Action {
                 id: importActionItem
                 text: "Import Images"