Split schema into separate schema and metadata files

Finders have both metadata (used for registering the artefact with
panopticon) and a schema (used to build the finder).

Previously, all this information was held in the one file -- the schema.
Now, it's held in two separate files -- `metadata/:slug.json` for the data
that should go on the artefact, and `schema/:slug.json` for the
schema itself.
Register Signup artefact with panopticon

For each finder, using its metadata hash, register a signup artefact
with panopticon.
Split presenters into separate files
Modify PanopticonRegisterer to be instantiatable
Merge pull request #55 from alphagov/split-schema-files

Register email signup artefact for each finder with Panopticon
Add date filtering for AAIB reports
Date filtering for CMA

Add date facet for the date opened on CMA
Merge pull request #56 from alphagov/date-filtering-aaib

Add date filtering for AAIB reports
Merge pull request #57 from alphagov/date-filtering-cma

Date filtering for CMA
Fix typo on CMA schema for date filtering

date_opened should have been opened_date
Merge pull request #59 from alphagov/fix-cma-date-filtering

Fix typo on CMA schema for date filtering
Remove Documents and Schema Registering

Now that we're using Rummager for returning the documents in a Finder,
we no longer need any of the tests related to any of this code. Also,
there is an issue with schemas being updated so we have now removed
registering the schemas, as they are now just used to serve the list of
possible facets for the Finder filters.
Merge pull request #60 from alphagov/remove-document-tests

Remove Documents and Schema Registering
Add initial documentation to finder-api

with @evilstreak @bestie @alicebartlett @themitchell
Remove mention of deprecated functionality

Now that we've entirely removed the ability of rummager to do anything
except serve schemas, it no longer acts as a search backend.

Remove any mention of this from the documentation.
Merge pull request #58 from alphagov/add-documentation

Add initial documentation to finder-api