Update the credits

Please let me know if I forgot someone in the relevant sections, as it's very likely the case.

• Move terencehill to the Core Team
• Create a "Campaign" section and add Mirio
• Add bones_was_here and Dr. Jaska to the "Game Code" credits
• Add Freddy to the "Website" credits
• Remove LegendGuard from the "Other Active Contributors" section, as they're now part of the Extended Team
• Add cityy to the Level Design credits (author of Fuse and Opium)
• Use my full name (already there in the list of French translators)
• Update the Translation credits (by using information available on Transifex and in the PO files), add the "Portugese (Brazil)" and "Turkish" categories since these languages are selectable in the game settings.