Added RDkit tool to calculate structural similarity between files.

[hechth]

Closes #746

Further additions could see implementation and support of tabular inputs with a specific column to identify structural information.

[bgruening]

@hechth isn't that this tool https://github.com/bgruening/galaxytools/blob/master/chemicaltoolbox/simsearch/simsearch.xml

chemfp supports RDkit fingerprints and similarity searches.

We also have this RDKit tool suite: https://github.com/bgruening/galaxytools/tree/master/chemicaltoolbox/rdkit

Let me know if you need this tool here and I will review.

[bgruening]

Here is the FPS tools, where FPS is a fingerprint standard file: https://github.com/bgruening/galaxytools/blob/master/chemicaltoolbox/chemfp/mol2fps.xml