MVP presenter for case studies

Just to get a failing test passing and learn something. Learned that generating
HTML from govspeak outside of a view context is going to be a whole heap of
fun...
Collection cache max age should be 5m

www.agileplannerapp.com/boards/173808/cards/8023

HMRC need to publish a collection page which needs
to reflect the latest changes in no longer than 5m.

made a change to the `CacheControlHelper` to allow
overriding the `cache_max_age` from the controller,
so that we can set a max age of 5m for collections.
Add organisation slug changer command
Add rake task and usage notes.
Cleanup unused image files

We no longer show screenshots on the pages of exempt organisations so these
images are redundant.
Cleanup old fall-back image for organisations

Before we had the ability to upload a default news image for organisations in
admin, we did a static files lookup. This code and the assets are now redundant
as default images have been uploaded for all the organisations in question.
Allow additional ArcGIS file format to be uploaded

www.agileplannerapp.com/boards/173808/cards/8154

permit files with ArcGIS file extension `.avl` to
be uploaded as part of collections. `.avl` are
ArcView 3 legend files.

whilst working on that area, i've just reformatted
the arrays to be more compact.
Allowable filetypes to support transition

Allowable filetypes to support department content transition; diff,
chm, sch, wsdl, xslt
Render the govspeak body as HTML
Rename test file to match thing it tests
Wire in case study representation

Case studies use their own representation when pushing to the publishing API so
we can use them as a test case through the new stack.
Refactor PublishingApiPresenter::CaseStudy

Remove the duplication between the presenters with inheritance
Tidy up use of LeadImagePresenterHelper

Removes duplication and make public/private interface clearer
Publishing API: Include an image for case studies

If the case study or it's org has an image available, we include it in the JSON
sent to the Publishing API.

Note that this code will not fall back to the "placeholder" image if neither the
case study or the organisation doesn't have an image. This is intentional as the
responsibility for deciding what to display if no image is available should lie
with the public-facing application that renders the content.
Rename first published key to match method name
Data migration to push case studies to content store
Register editions with panopticon as well as search

Panopticon stores the organisations associated with editions, so they
need to be updated in panopticon. We also changed to use the service
listeners to perform the indexing, as these have well defined behaviours
and are designed to be self-contained.
Use #find_each to iterate editions

there may be a large number of editions
Reorder filetypes

Reorder filetype lists alphabetically
Remove title separator line for freedom of information addresses