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".
Process broken links in batches

This change should speed up the report generation by 10x. Documents are
loaded in batches and processed 100 at a time by 10 separate forked
processes.