Remove stylesheets from html and include in js

The stylesheets that were linked in the index.html were redundant, as
they were already bundled by the webpack. The style.css was again imported in
the components/app.jsx. Now, it is placed in the index.js in a
order that style.css overrides the other stylesheets.

src/index.js

@@ -6,5 +6,6 @@ import './lib/codemirror/addon/fold/foldgutter.css';
 import './lib/codemirror/addon/dialog/dialog.css';
 import './lib/hint.min.css';
 import './lib/inlet.css';
+import './style.css';
 
 export default App;