Adding headline container

Adding a new container for the days headlines.
Allows for standard and big size stories only.

Logic is:
* 2 standard stories per column
* 1 big story per column
* Max 4 columns

# What?
### mobile
![mobile](https://cloud.githubusercontent.com/assets/31692/3746844/fb20b796-17c5-11e4-8339-35194ea4a0d5.png)

### desktop
![desktop](https://cloud.githubusercontent.com/assets/31692/3749300/525c6db0-17ea-11e4-911b-29cdb6d96a07.png)

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![Illusions](http://static.paulboxley.com/2014/monument_valley_penrose.gif)
(`.headline-list--#{$i}-big` and below)