Add mailers

[mattdowdell]

Mailers need to be implemented for the following actions:

• Send an activation email on login, see Implement activation emails #13.
• Send a password reset email on user request, see Reset password #14

For this to work in production, this also requires the creation of a new email user, e.g. noreply@altitude.tech.

• Account created.
• (more...)

Also needs SMTP credentials to be supplied.