Should be able to do things like this for message bodies: ``` Hey {{first_name}}, Thanks for applying! ... - The {{hackathon_name}} Team ``` Requirements: * [x] Secure. Can't be such a loose system that it could lead to security holes or syntax that would break the site * [x] Preview-able. For any supported variable, there should be a standard "example" value that's used while drafting the message. * [ ] Stretch goal: UI for defining custom variables