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/compose/components/search.jsx

@@ -36,6 +36,10 @@ const Search = React.createClass({
     }
   },
 
+  noop () {
+
+  },
+
   handleFocus () {
     this.props.onShow();
   },
@@ -56,9 +60,9 @@ const Search = React.createClass({
           onFocus={this.handleFocus}
         />
 
-        <div className='search__icon'>
+        <div role='button' tabIndex='0' className='search__icon' onClick={hasValue ? this.handleClear : this.noop}>
           <i className={`fa fa-search ${hasValue ? '' : 'active'}`} />
-          <i className={`fa fa-times-circle ${hasValue ? 'active' : ''}`} onClick={this.handleClear} />
+          <i aria-label="Clear search" className={`fa fa-times-circle ${hasValue ? 'active' : ''}`} />
         </div>
       </div>
     );