Feature GH-981: Add HOC banner component

[mewtaylor]

Implements #981.

A couple things to note about this from the specs:

• modals disappear for tablet and below (because the tiles in the banners disappear)
• The teacher banner, for teachers, will appear above the hoc banner

Test Cases

• Banner appears for logged in and logged out users
• Banner appears below teacher banner for teachers
• Tiles in banner show modal when the "see guides" part is clicked
• Modals disappear below our desktop breakpoint
• Tiles disappear below our desktop breakpoint

[rschamp]

My comment is more of a yellow than a red, so I think this looks good to go overall.

[mewtaylor]

@rschamp @chrisgarrity – for Nov 21 hotfix, we either need to not merge any December things into develop before Monday, or maybe create a separate hotfix branch (which would need to get PRs for the release branch too). Thoughts?

[rschamp]

@mewtaylor I think a hotfix branch would make the most sense. Can you explain what you mean about getting PRs for the release branch?

[mewtaylor]

@rschamp I mean that if there's a PR for a bugfix found during QA that needs to go against the release branch, I'll need to also open a PR against the hotfix branch that we create – unless we just don't merge this until after the release.

[chrisgarrity]

@mewtaylor @rschamp A hotfix branch makes sense to me, but I might wait a couple of days any any case to confirm the order of the tiles on the HOC banner.

[mewtaylor]

Going to re-open against release/hoc-nov-21