[ADD] Creation of a module to send documents via classical postal ways. ...

...This module uses the DocsAway web service. It allows to send single documents or multiple ones (thanks to selection in list views). Here, invoices and sale orders are ready to use

So far, this module is in debug mode (sending a mail doesn't really send one, but in the DocsAway account, you can verify the good reception of the mail). Once the review done, I will set it in production mode