Added support for the Process Engine to Frama-C for PKM, Frama-Clang for PKM,...

Added support for the Process Engine to Frama-C for PKM, Frama-Clang for PKM, ASFM for PKM (doc_to_asfm, asfm_to_doc, code_to_asfm), and UNISIM Excavator for PKM.
Changed the way PKM access keys are generated to enable duplicating PKM user's session.
Added /user/dup in the PKM REST API to enable duplicating the user's session.