Accessibility Starter Kit: Open Sentencing

### Background on the problem the feature will solve/improved user experience
Open Sentencing needs to improve its web accessibility to be more inclusive of our end-users.

### Describe the solution you'd like
To this end in this project we'd like to:

- [ ] perform automatic testing to assess Level 1 accessibility (see reference issue)
- [ ] document and fix issues raised by automatic accessibility testing
- [ ] address any existing accessibility Github issues in the various Open Sentencing repos
- [ ] perform additional manual tests and fix those as well

### Reference issues
- #53

Start by reading reference issue #53 and inspecting the accessibility-related issues across the Open Sentencing repositories. Determine the automatic and manual checks needed from the issue description; done means the checks are performed, findings are documented and fixed, and existing accessibility issues are addressed.

Written by the indexing model from the issue text.