Add confirmation and error pages with tests

[gmrabian]

Summary

• Add confirmation page and navigate to it upon successful form submission
• Add error page if form submission fails
• Add tests

Fixes #74

Type of change

• [x] New feature (non-breaking change which adds functionality)

How To Test

• Go to a form application (may need to add /apply from a details page while we work on routing)

• Type in anything and submit the form

• Verify it goes to the confirmation page (which will be built out later

• Navigate to /error

• Verify the error page shows with a link back home

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 d4a2fa36 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 82.3% (80% is the threshold).

This pull request will bring the total coverage in the repository to 96.2%.

View more on Code Climate.