breadcrumbs component

[gumaerc]

What are the relevant tickets?

Closes https://github.com/mitodl/hq/issues/4593

Description (What does it do?)

This PR adds a new Breadcrumbs component to ol-components. This component takes a variant of "light" or "dark," list of dicts in the ancestors property, each with an href and label property as well as a value for current which is just a string labeling the current page. The component is implemented on the various pages that use breadcrumbs.

Screenshots (if appropriate):

How can this be tested?

• Spin up mit-open on this branch
• Visit http://localhost:8063/units/
• Verify that the breadcrumbs load properly, and that the Home link goes back home
• Go back to the units page
• Click on any of the cards to visit a unit channel page
• Verify that clicking the MIT Units breadcrumb brings you back to the units page
• View some of the other pages that had their breadcrumbs updated:
  • About Us (http://localhost:8063/about/)
  • Privacy Policy (http://localhost:8063/privacy/)
  • Terms of Service (http://localhost:8063/terms/)
  • Departments (http://localhost:8063/departments/)
  • Topics (http://localhost:8063/topics/)
• View the storybook for the new component: http://localhost:6006/?path=/story/ol-components-breadcrumbs--story

[shanbady]

Looks good and works as needed. LGTM