Put pry in dev, for now

It is so useful to have in development for debugging
Use the data dump from ons_poc_data
Include how many observations dataset has
Remove dataset from obs presenter

We don't want it included at this level, as we'll be using observation presenter for multiple results.

Also added in some safeguards against assumptions about what an observation has, to prevent going BOOM if fields aren't there.
API returns multiple observations

This allows us to query /dataset/release/observations.json?product=thing

and get returned a json of all observations that match the query params
Fix measures

How we capture measure relationship has changed in the models, update tests and presenter accordingly.
TESTS

So, factory girl was doing my head in so I copied across(CP hacky, for now) from models as I know they work.

Fix up the cucumber tests to then find correct values.

Include new cucumber test for observation query.

My cucumber seems repetitive, sure there is a better way of doing this.
Merge pull request #11 from ONSdigital/date_slice

Date slice