Remove group name validation case sensitivity

For issue mentioned [here](https://meta.discourse.org/t/group-names-are-case-insensitive-can-be-duplicated-typed-wrong-in-invite-csv/23002/3)
Re-looking at it right this second, there's a potential issue with, say, a 19-character group name having to get an index tacked onto the end of it... groan... such edge case...