Add rules to enforce accessibility requirements

[LawnGnome]

We should look at pulling in something like https://github.com/danrigsby/eslint-plugin-idiomatic-jsx to define rules that prevent us from creating inaccessible elements.

Low hanging fruit here would include:

• Images must have alt attributes.
• iframes must have title attributes.
• Other things that should be added here!