Fix randomization for >1 epochs, keep counting up to avoid repeats.
Outsource Dropout class and its JUnit tests.
Minor cleanup, cosmetics.
Add JavaDoc comments for some methods (more to come).
Add a boolean flag whether to ignore constant columns.
Improve RNG seeding for old NeuralNet code.  And Fix typos.
Add helper to shuffle a Frame (chunk by chunk).
Add shuffling of training data as input option for NN.
Update NN JUnit tests.
Update Mnist NN samples for recent API changes.
Re-enable NN Spiral test.