send emails when MOU is signed

we build up one personalisation dict, and then pass it in to all the
different templates - so be careful editing things. also of note, we
check if the agreement_signed_on_behalf_of is set, and send a different
template with slightly different wording to the person who clicked the
confirm button.

app/models.py

@@ -346,6 +346,7 @@ class Organisation(db.Model):
         db.ForeignKey('users.id'),
         nullable=True,
     )
+    agreement_signed_by = db.relationship('User')
     agreement_signed_on_behalf_of_name = db.Column(db.String(255), nullable=True)
     agreement_signed_on_behalf_of_email_address = db.Column(db.String(255), nullable=True)
     agreement_signed_version = db.Column(db.Float, nullable=True)