Show a list of members that are part of a given membergroup.

• Adding or removing members requires either 'manage_membergroups' permission or group moderator status
• Tells you the group doesn't exist if it's hidden and you can't moderate it
• Does not allow browsing of guests, moderators or "Regular Members"
• Managing the Admin group requires the 'admin_forum' permission
• Calls removeMembersFromGroup to handle removing members