Add option to keep extracted files in subdirectory
Add option to keep extracted files in subdirectory

When extracting files from an archive the default behavior is to put them
all in a single directory for the dataset in the retriever's raw data directory.
This adds the ability to keep the files from each archive in a subdirectory
named after the archive. This makes it easier to place them in appropriate
subdirectories in final location when desired.

davharris/retriever,embaldridge/retriever,embaldridge/retriever,henrykironde/deletedret,goelakash/retriever,goelakash/retriever,davharris/retriever,henrykironde/deletedret,davharris/retriever,embaldridge/retriever