enhance(eslint-a11y): Enable the strict jsx-a11y

We're currently passing these, apart from those explicitly disabled.
https://www.npmjs.com/package/eslint-plugin-jsx-a11y#difference-between-recommended-and-strict-mode

.eslintrc

@@ -9,7 +9,8 @@
     "plugin:react/recommended",
     "plugin:flowtype/recommended",
     "plugin:import/errors",
-    "plugin:import/warnings"
+    "plugin:import/warnings",
+    "plugin:jsx-a11y/strict"
   ],
   "env": {
     "browser": true,