Dev

[tsackton]

This pull request closes #48:

• Uses SRA prefetch to speed up downloading where possible.
• If file is not available from SRA, tries to download .sra file from ENA using wget
• If that fails, tries to download fastq.gz files from ENA

If all attempts fail, the job will fail, but usually in this case more investigation is needed to figure out the source of the problem.

I have tested this on a few species and so far it seems to be working.