notififcation: Add Notification for Code Comment.
Merge pull request #425 from npcode/feature/noti-for-code-comment

notififcation: Add Notification for Code Comment.
user: Delete the old avatar after uploading new one.
fixed n2br markdown syntax randering for issue editor
code: Allow nonmember to comment on code.
avatar: change default avatar image
member request: fixed a bug

* deleting the member request which was submited befor adding it as a new member
notification: Delete it while deleting its source.
Merge pull request #427 from insanehong/issue/markdown-n2br

fixed n2br markdown syntax randering for issue editor