RDKit error handling

[jvansan]

The methods in views.py do not account for cases where RDKit raises an error rather than returns no mol object. Note, these are difficult to handle cases because the RDKit python bindings don't have the C++ errors that occur. In my experience, it necessary to handle these by catching TypeError exceptions.

I suggest either refactoring to call methods which have do exception handling, or to write a decorator which does this. I can do either of these if anyone has a preference.

[mwang87]

I think in these cases because the functions are short and cannot be recovered from, a decorator would be better. Thanks for the help Jeff!