Moving references to mixins, adding it to biosamples and donors
adding sample data for references in donor and biosample
Example PMID's should have no space in them
Had to add the references mixin to the inherited classes like human_donor
Removing doi as a reference type in the majority of the test set, I think the original regEx is broken
experiment schema also needed the mixin for references since it did not inherit from the dataset
Adding the correct sample for a doi in references
Merge pull request #226 from ENCODE-DCC/1266-Add_references

1266 add references