Add-ons Group membership moderators 2.3.0

• Require XenForo 2.3+.
• Require PHP 8.0+.
• Require Standard Library v1.21.0+.
• Add password-based confirmation when adding / removing users from a group.
• Minor code clean up.

• Only show 'Group Moderators' menu item if the user is a group moderator
• Added multi column layout in ACP for the list of groups

• In some situations the user was not removed properly from a group. This has been fixed.
• Rewrite of add/remove function
• Big Thanks @alleluia