Format person a little better if email is not set

Just noticed the string representation of a person comes out as "First_name Last_name <None>" if their email address is not set. I changed it to "First_name Last_name <>", but I could also remove the angle brackets entirely if you prefer.
Agreed: make this `email = ' <{0}>'.format(self.email)` and remove the `<>` from the line below.