Lsl helper allowed owner refactoring

Very minor refactoring of AllowedOwner logic mainly to finally get rid of the old misspelled 'AllowedOwnner'
Using case insensitive hashset to store and lookup owner uuids.
Duplicate and invalid UUIDs are removed from the owners list and a warning is presented if invalid UUIDs are detected
Renamed AllowedOwner to AllowedOwners. Not renaming "allowed_owner" setting to preserve backwards compatibility
LSLHelper Settings are saved when the settings window is closed. This is needed because it's very possible to edit the owner list and directly close the settings box, which will not trigger the 'leave' evet that is currently used to save the owners list.

cinderblocks / radegast