Tree-like view for examples

As mentioned in #492 , it would make the navigation easier to have a tree-like view of all the example categories on the left. This would replace the second box of filters. I think the GitHub PR files tab is a good example of how it can look like:


Start by locating the current examples navigation and the second filter box in the browser application. Review how example categories are represented and how the existing filters update the view. Done means the filters are replaced by a tree-like category view that makes example navigation easier and matches the requested GitHub-style interaction.

Written by the indexing model from the issue text.