Base group management 1.8 (Conflict resolved)

* Add group management librairy ( Add, Edit, Del )
* Add group management JS librairy (javascript for the multiselect drop/down )
* Include group management in frontEnd ( Add group management in nuked.php, Define new constants, Update array $user )
* Include group management in backEnd ( Use group access in design.php, Add group menu in design.php, Add CSS style for group admin page, Update user admin with group management )
* Add group management in installation
* Add colorPicker ( js, pictures )
* Resolved conflict in nkSessions.php