Add approve/deny buttons and display only approved comments

[dallasjc]

This pr is built on top of this pr: https://github.com/voteliquid/liquid.us/pull/187

• [x] Add approve/reject button to comment

• [ ] Finish activating approve/reject button after approval_status set in backend

• [ ] show only approved comments on bill/petition page, activity page, and user page after approval_status added to backend