[FIX] mail: encoding of sender name with unicode

When sending an email, both formats 'Name <email>' or '"Name" <email>' can be used for fields 'From', 'To' and others. If the name contains unicode characters, a regex only matching '"Name" <email>' was used to encode the name with RFC2047. That meant that the name was not encoded and eventually dropped, using only the email part.
Instead of using a limited regex, use the parseaddr method from email library.
Fixes lp:1272610, opw 607683