small bug here:
When pressing the "Select bones shown in the dopesheet" button:
- the bones are added to a selection
- the bones are not highlighted/selected in the tree view (bug?)
- any previous selection in the tree view remains/is not cleared (bug?)
By contrast, when clicking on a bone's name/row in the dopesheet:
- the bone is added to a selection
- the bone is highlighted/selected in the tree view
- any previous selection in the tree view is cleared and replaced by the new selection
