Perform accessibility audit

[kburk1997]

We need to perform an accessibility audit to make sure our application is fully accessible to people with disabilities.

Ideally, our project should meet the WCAG 2.1 guidelines.

If we find any issues during the audit, we should create GitHub issues for each issue we find, and tag it with the "accessibility" label.

[kburk1997]

Just started the audit on the homepage!
There is some missing alt text, which should be addressed once we finally get around to #152.
I found some known issues with contrast, which were noted in the yacs and yacs-web repositories as well.

[kburk1997]

Preliminary audit completed!
TODO: manually test with a screen reader