Tool to compare dashboards across environments

Assumes staging and preview currently, pass the slug as an argument and
it will request both and diff them.
Return errors as per JSON API suggestion

See http://jsonapi.org/format/#errors
Delete modules not provided on PUT

When a dashboard is updated and the 'modules' key is present but there
are modules linked to the dashboard that are not provided. Delete them!

This fits with the idea that PUTing a dashboard is pushing the resource
and is idempotent(ish).
Merge pull request #230 from alphagov/feature/json-api-errors

Return errors as per JSON API suggestion
Merge pull request #254 from alphagov/add-compare-dashboards-tool

Tool to compare dashboards across environments
Merge pull request #256 from alphagov/delete-modules-on-put

Delete modules not provided on PUT
Sort list of dashboards by title

Based on feedback, it would be better to have the list of dashboards
sorted by something. Right now I've decided to sort dashboards by
title, but if anyone has a need to change this sort they should
feel free to.
Consistently return JSON API errors
Merge pull request #257 from alphagov/sort-dashboards-by-title

Sort list of dashboards by title
Import schemas script

This has been tested on preview and locally against real data. All but
two modules are valid according to it and they are easy to fix. We
Should continue to only validate options as other flat fields are
already validated. There is an issue around the validation of the
availability module as it is always in the tab module so is not
currently validated.

Schemas are currently draft3 which necessitated some test and code
changes so these are not flagged as invalid.
Merge pull request #258 from alphagov/fix-typo

Consistently return JSON API errors
Merge pull request #259 from alphagov/clean-import-schemas

import schemas