Issue #266 Fixes problem when no voucher is checked to be printed. Rises a tooltip. But, even if the call was produced and no template was found in generate_for_vouchers, it would be redirected to the previous page (subject edit) or, if no previous page is found, to the subject list

Fixes most of #263 : nd number should have PDP prefix; screening numbers should be filled in (using P-) ; location prefix should be defined: P (CHL), F (Flying team)

added signals to Subject and StudySubjet. These signals fire after an instance is saved and check if the subject is excluded, resigned or dead and then call the methods that finish all the appointments and visits. It is safer than doing it on the forms or other parts of the code. Issue #203

Issue #259 : added test to send mail with general appointment and appointment types: test_kit_request_send_mail_with_general_appointment