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 
Relatively minor, but it will be a lot easier to read this if it is formatted a bit more, e.g.,:

```sql
SELECT EXISTS(
    SELECT filepath_id
    FROM qiita....
    WHERE foo = bar 
  UNION
    SELECT blah blah ....
```