Cleaning: Split core.php in two parts

[ Previous state ]

core.php loads the configuration, the core libraries and then provides
a lot of helper functions accumalated at the Espace Win era from 2001.

[ Current state ]

• core.php loads the configuration and the core libraries
• GlobalFunctions.php contains the global functions

[ Still to do ]

• Remove from GlobalFunctions.php anything we don't use
• Consider to create static classes to store families of functions