Fix broken link on Readme.md

Changed contribution guide to point to the file that is now in the main directory rather than the docs folder.
Merge pull request #1593 from kyconny/patch-1

Fix broken link on Readme.md
Add new Whitehall::BrokenLinkReporter

This version runs a LinksReport for each public edition and generates
CSV files listing those editions that have broken links, organised by
their lead organisation.
Cleanup old BadLinkReporter code
Update language around broken links

The notifier is sending "broken link" reports not "bad link" reports.
Rake task to generate/send broken link reports
Handle documents with no lead organisation

A Speech that has a person_override set do not have to have a lead
organisation. This updates the BrokenLinkReporter to handle this,
falling back to the first organisation available.
Handle documents with no organisations

It's technically possible for a document to be associated with no
organisations. This handles that case, putting the results from the
broken link checks into a separate CSV file.
Prevent libcurl connection resuse

The broken link reporter becomes unstuck after a certain number of
requests and starts reporting unresolvable host name for all links. Some
Google-ing suggests this is caused by connection reuse by libcurl.
Connection pooling is probably not a good idea with this volumn of links
and domains to check.
Add exception reporting to broken link reporter

So that we are alerted when the rake task falls over.
Timestamp broken link reports filename
Handle SupportingPage in BrokenLinkReporter
Modify language around organisations

The method name #lead_organisation is making less sense now as many of
the documents do not have a "lead organisation".
Slug change for UKTI Belgium.
Merge pull request #1594 from alphagov/ukti-belgium

Slug change for UKTI Belgium.
Increase links_reports.links limit to MEDIUMTEXT

The previous limit was too small to cope with the volumn of links on
some documents. This ups the limit of the column to that of a
MEDIUMTEXT.
Change slug for charity commission.

Data migration to update the organisation slug, and associated data,
create a redirect and reindex documents in search.

This also renames the org screenshot file so that it can continue to be
found.
Merge pull request #1596 from alphagov/charity_commission_slug_change

Change slug for charity commission.
BrokenLinkReporter handles CorporateInformationPage

These don't have a lead_organisation method either...
Merge pull request #1595 from alphagov/scheduled-publishing

Extract edition scheduled/unschedule service objects