Edit CR comments

As a Code Reviewer I'd like to be able to edit my comments so that I can correct my mistakes or add new info

• Given User has permission EDIT_OWN_POSTS, she can see Edit button and be able to change previously left comment.
• If User is not given EDIT_OWN_POSTS permission, she can't see Edit button.
• Given User is restricted from EDIT_OWN_POSTS, she can't see Edit button even if she is in another group which's allowed.
• Given User pressed the Edit button, she sees the same dialog as during leaving of the comment, but it's filled with previous text.
• The Editing dialog should contain Save and Cancel buttons.
• Given User edited a comment, the order of comments' displaying is not changing.

As a Moderator I'd like to be able to edit other's CR comments if someone posts inappropriate content.

• Given User is given EDIT_OTHERS_POSTS, she can edit comments left by other users.