Tweaks to Special:ListGroupRights:

Tweaks to Special:ListGroupRights:
* Have the internally-used permission key in parentheses after the descriptive text, since a primary purpose of the page is for sysadmins' convenience.
* Make sure to use the word "rollback" in rollback-related messages -- that's the name of the button, after all.
* Adjust the wording of a couple of other messages so they sound better or are clearer.