Create WDL workflow for Genbank submission

[dpark01]

Create a WDL workflow for ncbi.py prep_genbank_files (and the various prerequisite steps leading up to that) that can prepare an assembly for submission to Genbank. Pull assembly stats from WDL outputs (e.g. the outputs of the plot_coverage WDL task) instead of Snakemake outputs (e.g. pipes/rules/reports_only) for the submission metadata.

Workflow should be a single-sample workflow that takes an assembly (fasta), assembly metrics (see above), a reference genome (fasta), reference annotation (gb), and outputs an NCBI tbl file. Possibly an asn file too if the user provides an authors.sbt and other such prerequisites.