Organisation of football page extras

Sorry for the large pull request, I bumped into a few dragons on the way to my quest's end.

* Added accessible dropdowns
* As we are going to be adding fixtures to the football page, this is the start of making the rendering more understandable and less intrusive on the page.
* Added competition table on mobile

## Dropdowns
I ran into two problems:
1. having a nice dropdown
1. having said dropdown on the client

I could add the dropdown markup to the component sent down the pipes, but that would muck with it being embedded elsewhere (fronts). So we stick them together on the client.

The drop downs are also accessible and and work sans JS thanks to @kaelig's great idea from a few months ago.
You can have your own by using:
```
@fragments.dropdown("Deer species"){
<ul><li>Bambi</li></li>
<p>That's it really</p>
}
```

The reason for this was because of a [conversation with designers / devs around tables](https://github.com/guardian/frontend/pull/3830), where we keep landing in half way houses as design requirements aren't clear.

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![Done](http://31.media.tumblr.com/tumblr_m8037waAEP1rolf0zo1_400.gif)