Convert SBOL to SnapGene DNA files

[cjmyers]

The converter in libSBOLj has a new language "SnapGene" which creates SnapGene DNA files. To add support for this we need a new option on the validator front-end "Output SnapGene". This should set the language to "SnapGene" and support is needed on the backend to forward that command to libSBOLj.

[bbartley]

I have exposed conversion to SnapGene as an option through the pySBOL API. However, the HTTP call to the SBOL-Validator API currently returns an empty file. Just looking for confirmation that, since this issue is still open, I should expect this behavior.

[cjmyers]

@bbartley So support for SnapGene files is going to be very difficult. The validator is not currently well equipped to pass around binary files. They would need to be encoded, which means that the API will change. This will break all past uses of the API by pySBOL and others. How important is this feature to you?

[bbartley]

My near-term goal was simply to enable pySBOL users to access all the conversion formats that are currently supported by SBOL-Validator. SnapGene format is not at all critical. However, conversion to and from GFF3 using pySBOL is now supported, which fulfills the most critical need.

[cjmyers]

Great. We will lower the priority on this one then.