TreeNav: make the expanded version the default

We are investigating several tactics to address the issue of the icons in the main sidebar navigation not being very decipherable in the collapsed version. This is one way we will address it.

Start by locating the TreeNav component and its expanded and collapsed sidebar navigation behavior. Review how the default state is selected and verify the result in the UI; done means the expanded version is the default and the sidebar icons are no longer presented only in the unclear collapsed form.

Written by the indexing model from the issue text.