Rework left-hand nav order

[geriom]

Changes

A less intrusive attempt at reordering the left nav tree. This way we don't have to make any changes on each component repo, nor fundamentally change the way we build the site.

• Refactor config file for legibility
• Write new menu logic to pick manual menu from config file
• Replace spaces with dashes in folder names

/closes #338

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[geriom]

This implementation is completely different from #503 We can merge this one even before addressing the issue in that PR.

(sorry, posted it in the wrong PR a few minutes ago)