Information messages during time-requiring training procedures

Created by: laurentes

The stream bob::core::info was previously used to display information messages during iterative time-requiring training procedures, such as in the EMTrainer. Since recent changes occur in the way bob deals with I/O streams, these messages are not displayed anymore (at least through the python interpreter).

It would be nice to design guidelines for these kinds of procedures, explaining the way we should print such messages or at least providing the user an option to display them. We clearly lack of consistency accross the training submodule.