Multiple breadcrumb parent fields

[seth-shaw-unlv]

GitHub Issue: N/A

What does this Pull Request do?

• Exposes the breadcrumbs configuration in a form page.
• Allows the breadcrumbs builder to use multiple entity reference fields for finding parents
• Fixes a breadcrumbs builder error when the 'includeSelf' configuration is true.

What's new?

• Changes islandora_breadcrumbs.breadcrumbs schema to allow multiple reference fields instead of just one. Includes an update hook.
• Changes the breadcrumbs builder to use multiple reference fields the update config schema allows
• Added a form for updating breadcrumbs settings.
• Fixed an error that was causing the site to crash when the includeSelf option was true.
• Does this change add any new dependencies? No.
• Does this change require any other modifications to be made to the repository
  (i.e. Regeneration activity, etc.)? Run the Drupal database update to execute the update hook.
• Could this change impact execution of existing code? No.

How should this be tested?

• Create some nodes with the member_of field and verify the breadcrumbs work as expected
• Apply the PR
• Run the Drupal update (e.g. drush updatedb -y)
• Ensure the breadcrumbs are still working
• Change some settings on the new form @ /admin/config/islandora/breadcrumbs
• Ensure the changes work for the breadcrumbs
• Add another entity reference field
• Add that field to the breadcrumbs configuration
• Populate that field on a node and verify it is used for building breadcrumbs

Documentation Status

• Does this change existing behaviour that's currently documented? No.
• Does this change require new pages or sections of documentation? I don't think so.
• Who does this need to be documented for?

Interested parties

@Islandora/committers, esp. @jordandukart

[jordandukart]

Will try to get to this today @seth-shaw-unlv!