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 
This caught my attention, too -- when I talked to @josenavas offline, he said that basically there are only two states: transferring and not transferring.  If the current nomenclature confused both @wasade and myself, then maybe we should change the states to `transferring` and `idle`?