Video vpaid ui tweaks

Added an intermediate ui screen which displays until the advert is actually playing. Also removed video blocking divs that prevented a vpaid advert from being clicked on, and started using the native timing system provided by vpaid.
  
![screen shot 2014-12-10 at 17 59 20](https://cloud.githubusercontent.com/assets/4549425/5381111/41f3b9dc-8096-11e4-90e7-a2f314fc074b.png)