Rewrite nkSessions file + Update GroupManagement system

- Rename index in $user array
- Add Mods and Admin name access in $user array
- Delete all global in nkSessions
- Fix cookie Error on login
- Update checkAccess system for group management
- Update the call of $user array with $GLOBALS and new indexes
- Update the call of $cookie vars with $GLOBALS and new indexes
- Update some call of functions