Tutorial 2 RNN fix

[aribenjamin]

Hi! This includes the following changes:

• Plotting routine bugfix (wrong axes)
• In SimpleRNN, the nonlinearity is applied earlier (to make the variable firing_rates), and also the readout is from the firing rates
• The definition of dynamic_reg is changed to better match the paper
• To better match the paper's hyperparameters, the regularizers are divided by C and N ( hidden_size /num_conditions )
• Adam is changed to use no weight decay (which doubles up L2 reg)
• The definition of rectified_tanh is corrected.

With these changes the traces for SimpleRNN look like this: