Feature to import plasmid sequences in genabnk/fasta

* Imports FastA. Converts GenBank to FastA. 
   * Sequence stored in `feature`
      * `organism => 'Dictyostelium discoideum'`
   * An entry in `stockprop` for reference.
      *  `stockprop.type => 'plasmid_vector', stockprop.value => feature_id`
* Added test with 3 test data entries