ENH: allow users to delete their comments

/comments/user_delete/{{comment.pk}}/ POST request will allow users to
delete their own comments!

Here we used quite complex URL naming '../user_delete/'
Because, /comments/delete/{{comment.pk}}/ is by default provided by django
for moderators to remove comment
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

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

Example:
{% get_comment_list request.user 30 as comment_list %}

each comment is rendered in comments/comment_entry.html

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)