downloaded file unzipping and sorting

Data files downloaded from NSIDC come in a series of directories and subdirectories with long names. Amy's tutorial included some code for managing this structure and simplifying it to put all of the data files in one place. This code has been copied into the icepyx class object, but is not yet implemented (currently commented out). It would be great if this functionality were available, either as a step in the download process (where it currently is) or as a standalone method for the data class (probably the more flexible option).