[ADD] print, print_docsaway, print_sale : module to print and send docum...

...ents by post, implementation for docsaway webservices.

Print and send documents by post
print : provider base module to print account.invoice
print_sale : print and send sale.order
print_docsaway : implementation of docsAway Provider
If I understand your comment, you should define a mixin giving the field and the method. The code of print_validate_sending seems easy to factorize
- account.invoice -> self._name
- This invoice -> This self._description
- sent field: see below