Invoicing 2016

[theoo]

Remarks concerning invoicing 2016:

• add global pref to change the default mean of payment
• fix back button issue displaying text instead of the page
• allow mouse middle click on any listing
• fix quick add a receipt
• review all cancellation (affair and invoice), whether the object is offered or cancelled, and ensure it works as expected with subscription renewal
• name of the page should be more explicit than CIRCL, add section/subsection in it
• when clicking on an object (invoice or receipt), lead to the affairs page and point the object directly
• make "new forms" and "edit forms" visible. It's not always obvious for the client to see whether he/she's editing an object or creating a new one
• prevent editing of the "cancelled" boolean on invoice when the affair's status is "not invoicable"