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. 
You don't need to make this a property on `state`, since this is not used to render the component and isn't really a "state" of the component. If this changes, we don't want to re-render the component. You can just stick it as a regular property of the component onto `this`. Just do `this._previousTitle = document.title;`.

Also, you should never manipulate `this.state` directly but always use `this.setState` so that React has a chance to re-render.