Improve exact match in RDKit / notebooks

[madgpap]

We can make the RDKit exact match more like Symyx flex match There are 2 ways:

1. Turn on stereo match: set rdkit.do_chiral_sss=true; If we do this, some examples in Francis's notebook will not be accurate any more
2. Complement exact match with more flexible InChI match - again this can be documented in the chembl vs. mychembl notebook