ENH: Customization of tree widget height into xml

The height of the tree widgets/views can be set into the xml files.
It is done by adding a hint tag in the corresponding property.

Change-Id: I86b0ed22f4ebb7038e70dd2741d2e02192a758f6
Merge topic 'tree_widget_height' into next

6328f758 ENH: Customization of tree widget height into xml