Import gene sequences from fa.gz IGC file

Add script to allow loading of gene sequences from the .gz file that we can find here :https://db.cngb.org/microbiome/genecatalog/genecatalog_human/

manage.py import_igc_sequences /path/to/file.fa.gz

Needs to have genes created first. This might change in the future to perform directly creation of gene with sequences

Closes #98