WIP (Do not merge) Clarify dependencies

The purpose of this pull request is to:
- [ ] Clarify in the README which obligatory and optional dependencies CONCOCT has.
- [ ] Switch to anaconda as the recommended way of installing python dependencies
- [ ] Switch to miniconda as the way of installing dependenvies on travis
- [ ] Have a complete list of python dependencies in setup.py so pip can install CONCOCT through pypi.