Password Setter procedure has changed

[AlanSwenson]

This no longer works:

@password.setter
def _set_password(self, plaintext):
      self._password = bcrypt.generate_password_hash(plaintext)

Should be:

@password.setter
def password(self, plaintext):
      self._password = bcrypt.generate_password_hash(plaintext)

https://docs.sqlalchemy.org/en/latest/orm/extensions/hybrid.html

[AlanSwenson]

I can submit a PR if this is acceptable.

[AlanSwenson]

#112 is the PR for this fix