Show plugin name in document title

I think this is the most efficient way, so that the name only get's set when we fetch the plugin, and only changed back when the page is updated. Which, since it's React.js, shouldn't happen unless we move to a new page. 
nit: Ideally we set the title back to a previously cached title. Just in `updateTitle`, set a property `this.previousTitle` if it hasn't been set already.