Fix a typo.
Fix HEX-1340 "Neural Net: Labels on the score matrix are incorrect"

If the test set didn't bring its own categorical dictionary, then it fell back
to 1..N. Now, we ask the trained model for its categorical dictionary if it was
trained on data that contained the same column as the test data response
column.
Throw an exception if the response column is a constant class, do this for all models.
Rename column names to be unique.
Add a a copy of the iris dataset with 35 extra rows:
7 rows are multiplied 5 times, each containing one different empty column
Load new iris dataset with missing values.
Resolve HEX-1584: Handle datasets with missing values in Neural Nets.
Disallow ignored columns in Neural Nets for now (since it's not supported).
Merge branch 'arno-deeplearning' of https://github.com/0xdata/h2o into arno-deeplearning