Cleaned up code and comments in modules mnist_nnet_demost.py and data_pipeline.py
Added code for the denoising autoencoder tutorial to new file "tutorial_dA.py".

Added utils.py

Changed default number of hidden layers for the mlp net in mnist_nnet_demos.py from 500 to 1500.
Added code for the denoising autoencoder tutorial to new file "tutorial_dA.py".

Added utils.py

Changed default number of hidden layers for the mlp net in mnist_nnet_demos.py from 500 to 1500.