In training data add reactions with single product only for both 
published and unpublished reactions. Commented out the part where we 
add published reactions only generated by the retrostep. Now switching 
back to old approach of adding all published reactions of a chemical as 
reported in the database but this time only single product reactions are
added in the training data.
Merge branch 'master' of https://github.com/psuresearch/pca.git
merging with the git version