Copy frame name to middle click clipboard

User workflow requires single click frame name selection
in the FrameMonitorTree to copy to the QtGui clipboard,
updated to allow users this capability.

cuegui/cuegui/FrameMonitorTree.py

@@ -299,7 +299,8 @@ def __itemSingleClickedCopy(self, item, col):
         selected = [
             frame.data.name for frame in self.selectedObjects() if cuegui.Utils.isFrame(frame)]
         if selected:
-            QtWidgets.QApplication.clipboard().setText(" ".join(selected))
+            QtWidgets.QApplication.clipboard().setText(" ".join(selected),
+                                                       QtGui.QClipboard.Selection)
 
     def __itemSingleClickedViewLog(self, item, col):
         """Called when an item is clicked on. Views the log file contents