[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).
Nicely done on the Java7 style catch multiple.  Would this rather be `catch( Exception e) {` because *no matter what went wrong in sending, NPE or otherwise,* the desired handling is to log and ignore?