Upgrade to Django 1.7.1
Clean up threadedcomments

- conform to pep8
- fix tests

Ref #41
Use fix markup_tags

Use django-markup-deprecated and remove support for textile and rest
in comments.
Remove Creole and Textile markup languages
Install django_extensions

Among other things, it gives us the shell_plus management command.
Increase comments max length
Comment preview

Fix #41