[WIP] Multipage navigation

[MatMoore]

This branch is to try and get the navigation into a tree structure. The current live version is generated only from the index page, so most pages are not shown in the nav, and some pages are not even discoverable at the moment (like the resource lists)

Currently we are having problems with

• Some navigation entries having invisible titles
• It seems like everything shows up at the top level, instead of just the index, resources, and career path at the top level

However, we are missing the middleman metadata stuff at the top of each file, so that might be why it renders strangely. I'm also having trouble at the moment with middleman serve hanging which is stopping me from testing.

Changes on this branch

• Enabled the multi page and collapsable nav options
• Moved the "inspiration" page to the resources section since this shouldn't be a top level thing. This might have broken a link somewhere, but right now a lot of links are broken.

Next steps

There is a branch here with an example we can try and emulate: https://github.com/ConvivioTeam/paas-tech-docs/tree/GTD-14-prototype-multipage-navigation/source/troubleshooting/troubleshooting1

[MatMoore]

cc @deborahchua

[MatMoore]

Here's the issue for middleman hanging and a workaround: https://github.com/alphagov/tech-docs-template/issues/149

[MatMoore]

Closing in favour of https://github.com/alphagov/gds-tech-learning-pathway/pull/108