ENH: add edit comment feature

1. render edit comment form using template tag
2. $.ajax() is used for POST request
3. edit comment is opened in Bootstrap Modal
4. Submission Form is inherited from
django.contrib.comments.forms.CommentSecurityForm
ENH: show recent 20 user comments on profile

1. comments are generated using get_comment_list template tag
By default returns 20 recent comments; can also profile list count
explicitly

2. each comment is rendered in comments/comment_entry.html

3. send-email-icon-tiny (40 x 40 px) version of send-email-icon (64 x 64)
used for comments image (probably we need new image)