Add a11y tests for lesser-used pages

[cecilia-donnelly]

We have set up accessibility testing for the main portions of the application, but there are a few places that still need it.

Quoting from @PaulMorris in #518:

Here are the pages that will still not have a11y tests after PRs #676, #679, #684, and #686 land.

For service admin login
Pages for individual 'view enrollment'
Pages for organization and individual 'edit enrollment'
Pages for organization and individual 'renew enrollment'
My Profile page
Update profile page
Advanced Search page
Quick Search results page

For system admin login
Providers page
Service Agents page
Service Administrators page
System Administrators page
View User Account page
Edit User Account Page
Delete User Account Modal
Quick Search Results
Advanced Search Results

[PaulMorris]

Some additional pages not covered in the list above: For the provider role, we have full accessibility test coverage for the enrollment steps for "Head Start" (organization) and "Speech Language Pathologist" (individual) provider types, and that covers the majority of the pages in the enrollment steps. There are a handful of specialized pages that appear only for one or more of the other provider types, and these are not yet covered by the accessibility tests.

[kfogel]

Just ran across https://alphagov.github.io/accessibility-tool-audit/ (a comparison of automated accessibility checkers, updated as of April 2018) and thought I'd mention it here.