Seperate the callbacks, predefined_functions, and procedures in the MPIDB

[martinruefenacht]

Currently we track what mpi-binding block is what through the attrbutes. This should really be written to the MPIDB as separate mappings and not be required to take apart the entire description.

        for name, desc in dataset["procedures"].items():
            if desc["attributes"]["predefined_function"]:
                predef = PredefinedFunction(name, desc)
                PREDEFINED_FUNCTIONS[predef.name] = predef

            elif desc["attributes"]["callback"]:
                callback = Callback(name, desc)
                CALLBACKS[callback.name] = callback

            else:
                procedure = Procedure(name, desc)
                PROCEDURES[procedure.name] = procedure