Enable MCS to be more relaxed

[proteneer]

We currently enforce ring completion in the MCS protocol, we should probably switch to:

def mcs_map_simple(a, b, threshold: float = 0.5, timeout: int = 5, smarts: Optional[str] = None):
    """Find the MCS map of going from A to B"""
    params = rdFMCS.MCSParameters()
    params.BondCompareParameters.CompleteRingsOnly = 0
    params.BondCompareParameters.RingMatchesRingOnly = 0
    params.AtomCompareParameters.matchValences = 0
    params.AtomTyper = CompareDist(threshold=threshold)
    params.Timeout = timeout
    if smarts is not None:
        params.InitialSeed = smarts
    return rdFMCS.FindMCS([a, b], params)