fix vcfstats conda env

See merge request !8

explicitly put output of bc -l in variable.

Closes #29

See merge request !7

Fixes check of fraction.

marking python-dateutil without version as old python-dateutil version was completely removed from bioconda :-(

fastqc gives exit code zero and a corrupted
zip file on empty uncompressed fastq files.
The wrapper checks if the zip file exists. If so,
it checks its integrity. If that fails, it empties
the file. If the zip file does not exist, it
creates an empty file.

Fastq data in stats

See merge request !6