Add total counts, show user groups, allow sorting

[giuliomoro]

Nice to haves:

• add total count for discussions/posts
• show what group each user belongs to (e.g.: admin/mod/user)
• allow to sort for something else than name (e.g.: posts/discussions/last active/group)

[blackjelly]

1、hoping to add the function of the search user name,
2、the background statistics user registration number and display the user registration time
3、the user to delete, add, rights management.