Merge pull request #115 from MargaretLangley/master

prints_views changed to prints_screens
Merge pull request #116 from MargaretLangley/master

tabs to show view and listing in invoicings
sub_menu_folded? => sub_menu_state, invoicings bug always highligted invoicings
Merge branch 'master' of github.com:BCS-io/letting
invoice.back_page used to choose between back page or blank page. No-print shell round page to screen.