Last batch in deep methods

[antoinedemathelin]

Last batch should be of same length than others.
We should use .repeat and then .take to get same length dataset with same size of batch for all batches.

Additionaly, we may add .batch on validation dataset and a condition if .batch is already done.

Finaly we should look at the time needed to resize dataset coming from generator (as they have no length we should enumerate all the dataset to get the length...)