Prepare to enable react-a11y rules

When I first added these, I left TODO notes to come back and evaluate
enabling them. I've gone through and think that we should definitely at
least enable the rules that enforce basic spec compliance (e.g. that
props don't have typos and that all of the required props are provided
for the given role). Since these deal with basic correctness, I don't
think we need to add any verbiage to the style guide for these rules.

We still have some more that we should evaluate and decide about
enabling here, but this is a good step in the right direction.

Author: lencioni

packages/eslint-config-airbnb/rules/react-a11y.js

@@ -12,18 +12,18 @@ module.exports = {
     'jsx-a11y/aria-role': 2,
 
     // Enforce all aria-* props are valid.
-    // TODO: evaluate
+    // TODO: enable
     // https://github.com/evcohen/eslint-plugin-jsx-a11y/blob/master/docs/rules/aria-props.md
     'jsx-a11y/aria-props': 0,
 
     // Enforce ARIA state and property values are valid.
-    // TODO: evaluate
+    // TODO: enable
     // https://github.com/evcohen/eslint-plugin-jsx-a11y/blob/master/docs/rules/aria-proptypes.md
     'jsx-a11y/aria-proptypes': 0,
 
     // Enforce that elements that do not support ARIA roles, states, and
     // properties do not have those attributes.
-    // TODO: evaluate
+    // TODO: enable
     // https://github.com/evcohen/eslint-plugin-jsx-a11y/blob/master/docs/rules/aria-unsupported-elements.md
     'jsx-a11y/aria-unsupported-elements': 0,
 
@@ -69,13 +69,13 @@ module.exports = {
 
     // Enforce that elements with ARIA roles must have all required attributes
     // for that role.
-    // TODO: evaluate
+    // TODO: enable
     // https://github.com/evcohen/eslint-plugin-jsx-a11y/blob/master/docs/rules/role-has-required-aria-props.md
     'jsx-a11y/role-has-required-aria-props': 0,
 
     // Enforce that elements with explicit or implicit roles defined contain
     // only aria-* properties supported by that role.
-    // TODO: evaluate
+    // TODO: enable
     // https://github.com/evcohen/eslint-plugin-jsx-a11y/blob/master/docs/rules/role-supports-aria-props.md
     'jsx-a11y/role-supports-aria-props': 0,