Implements navigation setting, along with Primo/Alma navigation templates

[matt-bernhardt]

What does this PR do?

This adds a network-level configuration form for the theme, along with a second set of templates for the header nav and footer menu. The footer has also been split, now containing the overall footer.php file at the theme root, and a footer partial inside the inc/ directory.

The configuration form can now allow site builders to swap between two sets of site navigation: the first, and default, option is the current set of menus. The second set is for when we launch the new discovery tools next month.

Darcy and Stephanie have signed off on these changes from the stakeholder perspective, and the launch day steps to change this setting are on the project wiki's checklist.

Helpful background context (if appropriate)

You can see the mockups for the navigation in the linked ticket. This is one of a pair of tickets that will support the launch of Alma and Primo - the other (already merged) has provided a configuration form for the multisearch widget on the home and search pages.

How can a reviewer manually see the effects of these changes?

This branch has been deployed to the staging site. To see the configuration form, visit /wp-admin/network/admin.php?page=discovery-settings on the staging URL.

What are the relevant tickets?

• https://mitlibraries.atlassian.net/browse/IMP-2143 (design and mockup)
• https://mitlibraries.atlassian.net/browse/IMP-2145 (implementation)

Screenshots (if appropriate)

See mockup in IMP-2143

Todo:

• [x] Documentation
• [x] Stakeholder approval

Requires new or updated plugins, themes, or libraries?

NO

Requires change to deploy process?

NO

[matt-bernhardt]

The things being flagged as issues to fix in CodeClimate are either not new (the lines are new because some templates are being copied/moved to new files), or are IMO not worth fixing. I'm happy to discuss in more detail, however.