add gradient checking code.
change to accommodate gradient checking
remove weights from the class member and pass it as an argument in all functions
refactor code to accomodate gradient checking
change nn_runner to use the new apis
fix return bug in __get_indicator_vector
make changes to the predict function. Get activations from the predict function.
Compute arg max in the nn_runner script to get the accuracy.
fix cost function
complete gradient  checking