Navigation auto-collapse feature

This issue is to discuss the new auto-collapse feature of the Olio theme engine. It is pulled from [this discussion](https://github.com/danielgtaylor/aglio/issues/103#issuecomment-120872366) on another issue.

@danielgtaylor wrote:

> It will now attempt to close as many groups as necessary to display everything on the page. That means some groups may stay open, and the groups it chooses are determined by their height. It will try to close the smallest possible group to fit everything on the screen. If nothing can be closed to fit everything, then the largest item is closed and it tries again, until either it runs out of items or fits everything.
>
> If you make your window smaller and refresh the page, all items will get collapsed. If people have a very large screen, then they will see some of the items. The goal is to show as much as possible based on the window size at page load time.

@robbinjanssen wrote:

> That explains :) we're getting a bit offtopic here (maybe a separate issue?) but for the toggling i'd suggest that:
> - Look at the currently selected item (#resource-group-action in the URL) and toggle that one open
> - If nothing is selected and the items don't fit, toggle the first item(s) open until they no longer fit

Anybody else have any thoughts?

Start by reading the linked discussion and the proposed behavior in this issue. Then locate the Olio theme engine's navigation entry point and inspect how #resource-group-action is represented in the URL and how groups are toggled. Done means the auto-collapse behavior is agreed upon and implemented consistently for different window sizes and selections.

Written by the indexing model from the issue text.