Update server conversion function to GFF format
Update server conversion function to GFF format

The annotations within the metadata JSON is converted
to GFF format, with the main changes being the start
position is now one-based instead of zero-based and 
the forward/reverse strands are represented with "+" and "-".

The GFF format also includes a `seqid` and `type` key, but
this information is not available within the v1 metadata JSON, 
so they are not included in this conversion process. 
nextstrain/auspice,nextstrain/auspice,nextstrain/auspice