68637480 Comments: ability to update and delete

- added base edit and update functionality
- added comment permissions policy via pundit
68637480 Comments: ability to update and delete

- added Rspec checks on edit and delete comment
68637480 Comments: ability to edit and delete

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)