Options for edited stamp

[purpleraison]

It would be really nice if there were a couple options for the stamp that gets placed on the page after a person edits their post.

The options (similar to vBulletin) could be:

- Admin can turn on/off 'edited on' stamp for any/all usergroups
- admin can give permission to usergroups to allow them to check/un-check a box if they want to display the 'edited' stamp when editing the post (in that template view).