Add Discontinued investigation MAIB report type

Ticket:
https://trello.com/c/hlULXxFi/447-add-report-type-for-maib-discontinued-investigation
Merge pull request #317 from alphagov/add-discontinued-investigation-for-maib

Add Discontinued investigation MAIB report type
Added temporary fix for MAA regulatory articles

To ensure users searching for articles using RA code numbers without spaces can still find the info they're looking for
Merge pull request #318 from willguv/master

Added temporary fix for MAA regulatory articles