prototyping function for sidebar

[choldgraf]

This moves the sidebar generation logic into a Python function, instead of using a jinja template for it. It uses a recursive function to build sub-lists for children of a page. It also adds an option to include parents of a page, which sets the foundation for a "sidebar-only" version of the theme.

By default, no behavior will change, but this is the new sidebar code:

  {% set nav = get_nav_object(maxdepth=3) %}
  {{ nav_to_html_list(nav) }}

However, if we use the include_item_names variable then the top-level headers will be included in the sidebar. We can use this along with collapse=False to grab the full-site TOC if we wish:

  {% set nav = get_nav_object(maxdepth=3, collapse=False) %}
  {{ nav_to_html_list(nav, include_item_names=True) }}

results in:

As you can see, currently this results in duplicated top-level headers in the sidebar and topbar, but eventually this could be switched on with a sidebar_only config value or something like this, that would then remove the top-bar.

It also reduces a little bit of CSS redundancy (I think) now that we are using SCSS
What do folks think?

[choldgraf]

a friendly ping on this one...I know folks have other fish to fry, but I would appreciate a look at this, since it's a necessary step for me to build off of it in another theme I'm building

[jorisvandenbossche]

Done in #219