add option `--use-http` to kraken-build for downloading taxonomy and genomes from ftp.ncbi.nlm.nih.gov

[pmenzel]

This would help those poor souls whose network firewall does not allow FTP or rsync connections to outside server.

Basically it would change download_genomic_library.sh and download_taxonomy.sh to use the HTTP protocol for fetching files instead of FTP in the call to wget. It would also need changing in rsync_from_ncbi.pl

[KeyLllll]

@pmenzel Hello, I added option --use-http, but the error still persists. Do you know how to solve it? Thank you. It shows that "Downloading nucleotide gb accession to taxon map..."