Adding new flexible container

There is nothing new in this container, it is a cocktail of things that have been used before, namely:
* __Standard__: 3 in a row then the list view.
* __Big:__ same as news big
* __Very big:__ Same as [`featuresauto` first stories](https://github.com/guardian/frontend/blob/master/common/app/views/fragments/containers/featuresauto.scala.html#L44)
• __Huge:__ same as news Huge.


## Have a look anyway
![mixcontainer](https://cloud.githubusercontent.com/assets/31692/3781402/dc99eece-1995-11e4-8413-ac8a3cd657bf.png)

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![Uncontained](http://cdn.gifstache.com/2012/9/20/gifstache.com_2044_1348354800.gif)