feat(BPA-627): prints None when there are not hits

[areejalsheikh]

When there are no modules found in the genome it prints out None.

This way the module_paths.tsv file would persistently have 4 tab-seperated columns. Before this change, when there were no hits found, it does not print anything making the module_paths.tsv file of 3 tab-seperated columns.

Before:

$ less negative_enrichm_results/module_paths.tsv
Genome_name     Module_id       Module_name
<a-genome-name>      <a-module-id>     Custom 

After:

$ less negative_enrichm_results/module_paths.tsv
Genome_name     Module_id       Module_name
<a-genome-name>      <a-module-id>     Custom     None