Push CWL files.

This PR basically has:

• CWL code
• Fix for https://github.com/EBI-Metagenomics/emg-viral-pipeline/issues/12
• Fix for contig length filter for big files was using too much memory (Alex A. reported this), https://github.com/EBI-Metagenomics/emg-viral-pipeline/pull/9/files#diff-339f5a2c4d738fae9dcc004b9ea0487a
• Added travis for python scripts and CWL