Headline container very big

Waiting for [this](https://github.com/guardian/frontend/pull/5532) which will make the PR cleaner.

Adding a new volume to the headline container.
The headline container is very prescriptive (having spoke to @stephanfowler) unlike the new container.

* You can only have one very big
* If there is a very big, you can only have 2 bigs

If there are no very bigs, works as per usual.

Again, as per this project, mobile breakpoints will be worked out at a later date.

## Quick peek
### 1 VB
![1verybig](https://cloud.githubusercontent.com/assets/31692/3905322/1e888d14-22e6-11e4-8236-e71ec2d8be26.png)

### 1VB 1B
![1vb1b](https://cloud.githubusercontent.com/assets/31692/3905320/1e7e971e-22e6-11e4-9c79-e290bece51d3.png)

### 1VB 2B
![1vb2b](https://cloud.githubusercontent.com/assets/31692/3905321/1e84611c-22e6-11e4-8c43-22e7de5562d0.png)

---

![Size matter](http://www.fishingthebig50.com/wp-content/uploads/2014/02/reverse-1313397701_big_fish_vs_small_fish-1.gif)
See e6b02a4e8d145f1f7af8810a5358fd69853945cc, in which I changed the way we'll deal with tonal borders. Can you have a look?