Add validations to service slugs

Now validate for uniqueness and format.
Add index to Place name field.

Mongo barfs when trying to order by a non-indexed field when you have a
large amount of data.
Extract Point tests into separate file.
Improve callbacks to setup data_sets
Add more unit tests around adding data_files
Feature changes for background processing.
Add delayed_job
Process uploaded csv files in background.

This stores the raw csv_data on the DataSet model, and then uses delayed_job to process this in the background.
Fix user flow when CSV parsing fails.
Fix broken markup.
Hide data_set editor until processing is complete.
Fix scoping of controller error handlers.

They should not be public methods as they're not actions.
Remove spurious debugger call
Prevent activating a data_set until processed
Simplify setting of data_set versions.
Constrain the size of uploaded CSV files.

Otherwise we will exceed Mongo's document size limit.
Remove govuk_content_models

This should never have been using them.  In fact the only thing we were using from it was the User factory, which is trivial to replicate.
Migration to create the delayed_job mongo indexes
Rename activate! method to activate.

This better reflects its behaviour (it calls save, not save!
internally).
Update warning message for empty data set.

It will now only show when processing is complete to avoid confusion.