Start a message model with distinct types. Message db operations take an optional type.
Save thanks messages to the database.

* Add a save function to the message model.
* Add kudos-test.js
Add thanks to email digests.

* Add a new text digest email template
Do a horrible job at formatting the shout outs.
Merge branch 'thanks-emails'
Use urlize from nunjucks to urlize urls in emails.

Use this in the web templates to avoid another home grown solution.