Raw data status filepath removal

Modifications to the raw data object:
 - Added a status to the raw data, to know when the files have been uploaded or they are being uploaded.
 - Added a function to remove all the filepaths associated from the RawData `clear_filepaths`
 - Added a function to remove a filepath from the RawData `remove_filepath`

Adds the needed bits for #548 
AFAIK, the filetype `directory` is only used to expose the result of an analysis job (i.e. PCoA plots) and the files inside that directory should be never be referenced from any other place in the DB. In fact, if they are, they are also moved/copied from that folder to the directory structure controlled by the DB. So that situation never happens.