Fixing neglect to determine whether a user has the permission to create a topic on a category (besides being able to create a post) in ListController, TopicList, and TopicListSerializer causing the "Create Topic" button to appear even if a user cannot actually create a topic in that category but can reply to a topic therein.
Merge pull request #1673 from aperrault/patch-04

Fixing neglect to determine whether a user has the permission to create ...