[ui] Viewer3D: TransformGizmo - add picking and transformations

- For now, transformations do not take well in count the orientation of the mouse but gizmo is functional.

meshroom/ui/qml/Viewer3D/TransformGizmoPicker.qml

@@ -0,0 +1,30 @@
+import Qt3D.Core 2.0
+import Qt3D.Render 2.9
+import Qt3D.Input 2.0
+import Qt3D.Extras 2.10
+import QtQuick 2.9
+import Qt3D.Logic 2.0
+
+ObjectPicker {
+    id: root
+    hoverEnabled: true
+    property bool isPressed : false
+    signal pickedChanged(bool picked)
+
+    onPressed: {
+        root.isPressed = true
+        pickedChanged(true)
+        mouseHandler.currentPosition = mouseHandler.lastPosition = pick.position
+    }
+    onEntered: {
+        material.ambient = "white"
+    }
+    onExited: {
+        if(!isPressed) material.ambient = baseColor
+    }
+    onReleased: {
+        material.ambient = baseColor
+        root.isPressed = false
+        pickedChanged(false)
+    }
+}