Show fewer items on mobile before hiding behind "Show More"

Limits it to 6. As it's defined in Scala once we move away to better definition of containers (instead of just slices) in the Scala code, we can easily up that limit for the news container.

@phamann I simplified the JS a bit. Hopefully I didn't break anything in the process :grinning: 

![screen shot 2014-09-22 at 17 01 55](https://cloud.githubusercontent.com/assets/1001642/4359444/dea9c59a-4271-11e4-801e-6d35531746dd.png)

![screen shot 2014-09-22 at 17 02 11](https://cloud.githubusercontent.com/assets/1001642/4359446/e2fc2ff2-4271-11e4-8e9f-6d7ee7d5eac7.png)

These classes should actually be modifiers: i.e. `.fc-show-more--hide-on-mobile`