MACS2 wrapper

This PR adds wrappers for MACS2 https://github.com/taoliu/MACS.

The first MACS callpeak wrapper is published in http://www.biomedcentral.com/1471-2164/14/494 and hosted here
https://github.com/modENCODE-DCC/Galaxy. Because the initial wrapper was published I think it's worth, and actually I promised Quang M Trinh, to mirror the code in his repository as well and update the ToolShed wrapper  https://toolshed.g2.bx.psu.edu/view/modencode-dcc/macs2. It would be nice if we could just redirect ToolShed repositories in such cases. Until we have such a feature I try to update both repositories.