Add i18n support

Make the "Running on.." string translatable and copy the extraction and
conversion of JSX and PO files from Cockpit.

src/app.jsx

@@ -21,6 +21,8 @@
 import cockpit from 'cockpit';
 import React from 'react';
 
+const _ = cockpit.gettext;
+
 export class Application extends React.Component {
     constructor() {
         super();
@@ -35,7 +37,7 @@ export class Application extends React.Component {
             <div className="container-fluid">
                 <h2>Starter Kit</h2>
                 <div>
-                    <span>Running on {this.state.hostname}</span>
+                    <span>{ cockpit.format(_("Running on $0"), this.state.hostname) }</span>
                 </div>
             </div>
         );