[Tensorboard] Log text prediction in evaluation

A very useful tool in order to understand model performance beyond obtaining loss: Actually show what are the predictions.

It'd be very useful to be able to "see" the output of the model during evaluation in text format. These should be logged in tensorboard. Tensorboard likely supports markdown style where you can put prediction in bold.

Maybe we can only print out the first batch as we should get a good amount of example from it.