Add elapsed time-based restriction to Edit Own Comment permission

Own Comment Editing is great for a typo recognized a few minutes after a comment is added to an issue, but presents a real hassle when it is used days or weeks after other comments have already been added to the issue. The webview of the Issue doesn't show a revision history for comments, nor does it show up in the Project activity stream, so the editor's new information may not make it to previous consumers of the comment.

Consider adding a permission that allows editing a comment for a configurable number of minutes after it is made, but then denies that ability. I'd expect to be able to configure that permission on a per-project basis.

(And yes, this can be handled with agreements between users as to when comments should be edited, however the edit button is always there so mistakes are easy to make.)