Replace print statements by logging in config, costs and dataset get folders

After the fail attempt to replace print statements in the pull request #684 resolving issue #41 due to casting and no printing problems, here a pull request with a small subset of pylearn2.

I choose, as a way to standardize logging formatting, to use [string.format](http://docs.python.org/2/library/stdtypes.html#str.format). It works with any type we pass as argument to the format function, as opposed to the modulo operator, and we also can change easily the order of the printed object. The drawback is that it's only compatible from 2.6 and I don't know if it's a problem or not.

Furthermore, in some part we find a comma after some print statements to avoid adding a new line at the end but this functionality isn't supported in logging so I make it work with a list and a join operation.

I didn't test the way it prints because I don't know if it's really necessary and I don't know how to this correctly. 
About the logging level, what is the solution? I think keeping prints instead of logger.info could be a good idea but, then, where do we use logger.info and debug?