Left and right arrow keys in tree-type lists

Summary:

Arrow keys do nothing in XML editor.

Steps to reproduce:

• open Inkscape
• Go to XML Editor
• Select a tree element and press left or right arrow key

What happened?

• Nothing

What should have happened?

• The list should collapse/expand with the left/right arrow keys respectively.
• Pressing the left arrow key on a (collapsed) element should move to it's parent.

Maybe:

• Pressing the right arrow key on an expanded parent might move to the first child.

Scrolling around a large list is frustrating. Going directly to the parent element would be a nice enhancement.