Adding a welcome email for new users.

Added the infrastructure necessary to support sending a email to
users when they sign up, either locally or by using an OAuth
provider. Also added a basic welcome message for new users.

Fixes #374
Addressing concerns with prior commit.

* Adding a link to the system to the text notification.
* Removed unnecessary lookup for email address from preflight.
* Moved dup welcome email code into a helper method.
Removing unnecessary parameter to email generation.
Merge pull request #401 from DavidEBest/devel-welcomeemail

Adding a welcome email for new users.