Add support for sending an e-mail programmatically

On a recent tech challenge, we were asked to send a "notification" from one user to another user, so the recipient knew to log in and take action. This is often in the form of an e-mail, and that's a piece of functionality that should be baked into TCP so it's available if we need it.

There are several 3rd party API-based platforms that support this. A free account should suffice, and new accounts could be made for each TC - the goal here is to add a service that can connect to the external API and fire an e-mail given:

- Recipient e-mail address
- Subject text
- Body text