Fixes permissions problem from proxy class

Hello there,

Just been doing some testing and found the proxy FluentComment class is causing permission problems.

To replicate:
- Create a group with all comment permissions
- Add a user to the group
- Login a user and verify that you can't see the fluent_comments app in admin

The problem seems to stem from here (https://code.djangoproject.com/ticket/11154) and the fix below allows users with correct permissions to access the fluent-comments app.  

I'm not completely convinced that the proxy needs to create it's own permissions but for now this at least fixes the issue.

Let me know what you think - sorry for breaking functionality with the proxy!