Better handling of Solidity compliation (#4860)

* Better use of SW

* Safe-guard against pending SW register bug (in Chrome)

* Added a simple Worker for Solidity compilation

js/src/views/WriteContract/writeContract.js

@@ -105,7 +105,7 @@ class WriteContract extends Component {
               className={ styles.editor }
               style={ { flex: `${size}%` } }
             >
-              <h2>{ this.renderTitle() }</h2>
+              <h2>asd{ this.renderTitle() }</h2>
 
               <Editor
                 ref='editor'