Add eslint-plugin-jsx-a11y (#1651)

* Add eslint-plugin-jsx-a11y.

* Fix npm script.

* Adjust npm scripts so test also runs lint.

* Fix existing lint errors.

* Don't break on a11y issues.

* Add role and tabIndex.

* Add vim and Mac files to .gitignore and .dockerignore.

* Handle htmlFor (partially), a that's actually a button.

* Fix missing tabIndex.

* Add cursor:pointer to load-more

* Revert change to load_more.

* Fixes based on review.

* Update yarn.lock.

* Don't try to install fsevents on Linux (hides warning noise).

app/assets/javascripts/components/features/notifications/components/setting_toggle.jsx

@@ -14,8 +14,8 @@ const labelSpanStyle = {
   marginLeft: '8px'
 };
 
-const SettingToggle = ({ settings, settingKey, label, onChange }) => (
-  <label style={labelStyle}>
+const SettingToggle = ({ settings, settingKey, label, onChange, htmlFor = '' }) => (
+  <label htmlFor={htmlFor} style={labelStyle}>
     <Toggle checked={settings.getIn(settingKey)} onChange={(e) => onChange(settingKey, e.target.checked)} />
     <span className='setting-toggle' style={labelSpanStyle}>{label}</span>
   </label>
@@ -25,7 +25,8 @@ SettingToggle.propTypes = {
   settings: ImmutablePropTypes.map.isRequired,
   settingKey: React.PropTypes.array.isRequired,
   label: React.PropTypes.node.isRequired,
-  onChange: React.PropTypes.func.isRequired
+  onChange: React.PropTypes.func.isRequired,
+  htmlFor: React.PropTypes.string
 };
 
 export default SettingToggle;