[UP-4149] Update the create tenant workflow to send a custom email inste...

...ad of using the reset-password email.

Moved the guts of the code to generate and send that email to a more generic notification interface so that I could wire up 2 different impls and potentially eventually support other notification methods (eg. SMS).
This method looks stateless.  Extract into a static method in a stateless helper class?  Or maybe `IPerson` should be exposing a `getEmailAddresses()` syntactic sugar to encapsulate this?