Ignore MRSs that cannot be converted

[goodmami]

From delph-in/pydelphin#319 and the related discussion on the developers-list, this issue is for improving robustness for MRSs that cannot be converted to EDS. The conversion happens here, but it would probably be easier to replace the from_mrs() calls with a custom, locally defined function that checks for conversion errors. Since skipping faulty items can make the score look better than it is, these should raise warnings, and maybe be optional. E.g.,

def eds_from_mrs(m: MRS, skip_on_errors=False) -> EDS:
    try:
        e = from_mrs(m, predicate_modifiers=True)
    except Exception:
        if skip_on_errors:
            warnings.warn(...)
            e = None
        else:
            raise
    return e

The Exception should really be EDSError but, as seen in the linked PyDelphin issue, conversion errors are not reliably EDSErrors.