Implemented the cdp.exp_info.from_xml() method to correctly restore the experimental info structure.
This fixes bug #22704 (https://gna.org/bugs/?22704), the corrupted relax state files after setting
the relax references via the bmrb.software, bmrb.display, or bmrb.write user functions.
This custom ExpInfo.from_xml() method is required to properly recreate the software, script and
citation list data structures of the cdp.exp_info data structure, as these are special RelaxListType
objects populated by Element objects (both from data_store.data_classes).
