[ui] GraphEditor: trigger fit on project opening

* fit when the underlying graph has changed (new/open project)
* add 'F' shortcut to fit
* trigger fit after UI has been fully initialized (correct sizes)

meshroom/ui/qml/GraphEditor/GraphEditor.qml

@@ -21,6 +21,16 @@ Item {
     signal workspaceClicked()
     signal nodeDoubleClicked(var node)
 
+    // trigger initial fit() after initialization
+    // (ensure GraphEditor has its final size)
+    Component.onCompleted: firstFitTimer.start()
+
+    Timer {
+        id: firstFitTimer
+        running: false
+        interval: 10
+        onTriggered: fit()
+    }
 
     clip: true
 
@@ -49,6 +59,12 @@ Item {
         selectNode(nodes[0])
     }
 
+
+    Keys.onPressed: {
+        if(event.key === Qt.Key_F)
+            fit()
+    }
+
     MouseArea {
         id: mouseArea
         anchors.fill: parent