Allow command line specification of type to republish
Allow command line specification of type to republish

`bin/republish_documents` => republishes everything
`bin/republish_documents aaib_reports` => aaib reports only
`bin/republish_documents flibble` => raises

alphagov/specialist-publisher-rebuild,alphagov/specialist-publisher-rebuild,alphagov/specialist-publisher-rebuild,alphagov/manuals-publisher,ministryofjustice/specialist-publisher,alphagov/specialist-publisher,alphagov/manuals-publisher,ministryofjustice/specialist-publisher,ministryofjustice/specialist-publisher,alphagov/manuals-publisher,alphagov/specialist-publisher,alphagov/specialist-publisher,ministryofjustice/specialist-publisher,alphagov/specialist-publisher-rebuild