Allow Pre-built BLAST database

[averagehat]

Description of feature

Currently the pipeline only accepts a FASTA file for blasting purposes--requiring the blast database to be created for each pipeline run. This is impractical for large databases.

[Joon-Klaps]

Hi @averagehat, you are completely right. Someone recently suggested the same thing on slack. I'll make sure it gets supported in the next release.
This release is taken a bit longer due to the conversion to the strict syntax of nextflow.