genomics:  separate genomics commands from core commands

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
biosal: add a minimum coverage option to spate

A great amount of time is spent on vertices with
a sequencing coverage of 1.

55708221328 / 70594590349 (0.7891) canonical vertices
have a coverage of 1 in the DOE Iowa Continuous
Corn Soil Metagenome.

This patch changes the minimum coverage to 2, and
this code will be modified to provide a runtime option
too.

Link: https://github.com/GeneAssembly/biosal/issues/723
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>