Completed JSON <=> Scala serialisation process. Implemented ANNEXE,
DIVERS and more formatters. Fixed JSON reading process by fixing and
simplifying getMixedcontent funtion. Implemented more simple test cases
to read JSON format. 
LEFT TODO: 
1) rename MIXED-CONTENT tag to VALEUR and have this validated by Guy.
2) implement more JSON read test cases to cover all ELFIN data.
3) most certainly correct list of nodes read/write to JSON encapsulating
Json.obj instructions in into Json.arr: Json.arr( Json.obj( ... ) )