[READY] Multi request

## Polling

We've exposed a `poll` class property on the  `Alephant::Broker` to be used inside the election-data-component cache like so:

 ```rb
# config.ru
Alephant::Broker.poll = false # tells Broker to send back a 420 status and X-Stop-Polling header
run Alephant::Broker::Application.new(BBC::Cosmos::Config.app)

```

## Data objects

To allow the storage and delivery of data objects, we've modified the component class to use the changes to the [alephant-cache](https://www.github.com/bbc-news/alephant-cache) which allows us to grab not only the content but the content type, so we can pass this back to the client.