Discussion Forums

A pretty simple implementation of discussion forums.

Still left to do:

1. Error messages on topic create validation fail (seem to be missing on other forms as well)
2. Some form of permissions (maybe you have to be enrolled in a class to post)
3. Topics allowed to be categorized under capsules as well as courses

Still should be fine to merge as long as these are fixed eventually. Let me know if you have any questions or if I need to change anything.