68637480 comments ability to edit and delete

https://www.pivotaltracker.com/story/show/68637480

- added base edit and update functionality
- added comment permissions policy via pundit
- added Rspec checks on edit and delete comment
- added Rspec checks for permission rules:
  - check on comment owner
  - check on time passed (comment can be updated or deleted only in 5 minutes after posting)
Merge pull request #51 from bitzesty/68637480-comments-ability-to-edit-and-delete

68637480 comments ability to edit and delete
6800299 comments ability to reply

Replying to comments in content planner
https://www.pivotaltracker.com/story/show/68002996

- added base reply comment functionality
- added reply email notification
- added permission policy for reply
  - added comment replies page
    - this page displays parent comment and all replies
    - user can add one more reply on this page
    - we will redirect to this page from mailer
  - added Rspec checks for:
    - review replies
    - reply from commentable association
    - reply from comment replies page
    - covered reply comment email notification with Rspec