Add 300x1050 MPU in right hand coloumn

For US edition only

It's mind-blowingly big, but will only ever be used in a few, very exceptional campaigns. Without it, we're excluded from conversations with advert agencies, even if it's not actually used.

To counter the size, we remove the Most Popular component if it's served. And for this to work, I've added a promise library, so our ad code knows when the most popular component has loaded and remove it

![1331055494_sniper_rifle_recoil](https://cloud.githubusercontent.com/assets/74132/4740343/4458f2e2-5a0c-11e4-8632-a7cff68b2e28.gif)