First round of accessibility fixes

[gmrabian]

Summary

1. H1 appears as top item on apply and confirmation pages
2. Single
   tag pair on each page
3. "Apply" and "View more" buttons now state which institution they go with (e.g. "Apply to Penn State University")
4. Details page uses h2s for card titles and h3s for large black text
5. Required application fields have text (required) after the field name
6. Essay question guidance appears once above all essay questions
7. Spinner has text indicating content is loading
8. Main navigation has a clear name: "Main navigation" instead of main-header-nav navigation

Fixes #167

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)

How To Test

• Verify above items live in this PR

Checklist:

• [x] My code follows the style guidelines of this project and has no linting errors
• [x] I have performed a self-review of my code
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation, including any applicable ADRs
• [x] My changes generate no new warnings
• [x] I have added tests that fail without these changes
• [x] New and existing tests (unit, integration, accessibility) pass locally
• [ ] Documentation updated
• [ ] If there are security concerns they are addressed or ticketed after being discussed

[codeclimate[bot]]

Code Climate has analyzed commit 68d0d9f8 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (80% is the threshold).

This pull request will bring the total coverage in the repository to 86.1%.

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