Merge branch issue#126 with master

Issue#126

• The superadmin group allows to navigate every project, run and analysis on nG6, hidden or not, with admin rights.
• There is a new table in the admin section ( Administration > Admin management ) that allow superadmins to add and remove users to and from the superadmin group.
• The group's key is NEVER written directly in the source code, allowing an easier deployment for production use.
• The only requirement outside of the source deployment is to create a group with title = 'ng6_superadmin'. For additional informations, check the SQL file.