Add Features statistics in Tensorboard

[vlomonaco]

We need to add some features statistics in tensorboard. The user should be able to specify them during the creation of the tensorboard object. For now the TensorboardLogging object is created in eval_protocol.py

[AndreaCossu]

Do you mean something like a running average and standard deviation of the input patterns features?

[vlomonaco]

I was thinking also at intermediate layers!