787 - Comment creation responses should include profile picture URLs

This regression was caused because we were using the PrincipalsDAO rather
than the PrincipalsUtil. The Util is responsible for adding signed profile
picture URLs.

It seems like comments and discussion messages are the only places
that are currently taking the user object from the request context and
returning it in the response.
787 follow-up

 * Added custom profile pics
 * Checking profile urls when retrieving messages
 * Added jsdoc
Reverted PrincipalsUtil in the authentication init and using PrincipalsUtil when creating messages
Merge branch '787-profile-pic' of https://github.com/simong/Hilary into 787-profile-pic
Extended the profile picture tests for commenting