Type E loans now require a sub-category at loan entry

All existing Type E loans have a sub-category of 'Overdrafts'
Type E is now called `Revolving Credit Guarantee`.
Add loan sub-category to reports and exports
Add loan sub-category to loan details page
Add loan sub-category to information declaration
Merge pull request #217 from alphagov/loan-sub-category

(Phase 6) Type E loans sub-category