Fix loadIris

- Use map lookups vs. list lookups 
- Use significantly less memory by allocating only as much as needed

 INDArray ret = Nd4j.ones(to, 4);
vs. 
INDArray ret = Nd4j.ones(to - from, NUM_FEATURES);

- Comments
- Code cleanup

Note: A lot of this code is quite generic for CSV style data and could be refactored in a different PR.