Add forums feature for website

[wihobbs]

Implement a feature that allows users to create "forums" to discuss books, similar to Reddit, but germane to a book that is listed (even if out of stock) on the bookstore website.

Need:

• Create a forum, which generates a new page for that forum, and links it on the "forums" page
• Reply on the forum, which is a feature only available to authenticated users
• Read through forums, and read an individual forum, which is available to all users, authenticated or not.
• Mark some forums as "employees-only," where the forums are created by employees, and only available to view if a users is an "employee" or "admin"

[wihobbs]

Employee-only forums and replies get kicked to next milestone, but all the other tasks were addressed in #130