Commercial: move Article's right MPU into javascript

We should not be (css) hiding adverts at certain breakpoints, as it give a false ad impression

In this case, we were only showing the right MPU on articles at breakpoints > tablet landscape.

I've removed the hard-coded slot, and we now create the slot with JS only if the column is visible

Downside is if the page is initially loaded at tablet portrait, and then rotated to tablet landscape, the advert will not be there. We can look into this in the future

![1327602286_cute_bichon_frise_puppy](https://cloud.githubusercontent.com/assets/74132/2789787/df5907d4-cbb2-11e3-992c-2be38e6f90f6.gif)