All emails. Code tidy

- Integrated forgotten password email. Tidied up
ForgottenPasswordResponseMaker
- Integrated account password changed email
- removed sending of password back in API response (previously this was
debug info due to the lack of email)
- New email classes for forgotten and change emails
- Mandrill client now accepts message type to determine which endpoint
to use
- registration email now sends ‘message’ as type rather than
registration
- New HTML templates for new emails