Describe behaviour of new roll call introduction field on fatality notices
Implement new roll_call_introduction field on FatalityNotices

It's not a mandatory field, but we're making sure we populate it in factories regardless.  Maybe it should be mandatory, but it's not clear what the data migration step should be for all existing fatality notices.
Don't show roll call introduction if it's missing
Make FatalityNotice#roll_call_introduction mandatory
The fatality notice importer now requires a roll_call_introduction field
Merge pull request #131 from alphagov/roll-call-info-on-fatality-notices

Roll call info on fatality notices