Fix plugin calls
The beforeSend plugin event is only called right before the response is sent. Since it was not called from the client.js after rendering, the cached contents were still containing the script tags that removeScriptTags.js should remove. Since it doesn't work on zipped contewnts, the zipped contents still contained the script tags. This is fixed by introducing a postRender plugin event which is called both before sending the response and after the phantom js sends the rendered page to the client.js.