Implement APIs and process for managing site data

See #3, #4 
The actions of this function are such that they are probably worth documenting (or else reducing functionality, so less explanation is needed).  Perhaps something like:

    """Return the path of the metadata file.
    If path is a valid file ending in .csv, return it.
    If path is a directory, return a path to {path}/metadata.csv.
    Otherwise, assume the path is a compressed archive, extract the
    archive, and return the path to metadata.csv within the archive.
    """