Cleaned Content model
Cleaned Content model

- Removed dead code
- Made set_username private
- Replaced double quotes with single quotes

edx/cs_comments_service,Stanford-Online/cs_comments_service,edx/cs_comments_service,edx-solutions/cs_comments_service,EDUlib/cs_comments_service,EDUlib/cs_comments_service,Stanford-Online/cs_comments_service,Stanford-Online/cs_comments_service,edx-solutions/cs_comments_service,EDUlib/cs_comments_service,edx/cs_comments_service,edx-solutions/cs_comments_service