Include automatic code quality checks

I'd like to propose automating code quality checks for PyTango. I have two ideas:

1. Include running flake8 in Travis build. Sardana has already implemented this and we can benefit from their experience by looking at: a) this PR that introduced flake8 to Sardana, b) that PR which made its output more readable.
2. Setup Codacy. I've made a test run of their checks for PyTango and its available here. Also, tango-controls account already exists there (but I don't know who manages it) and it's enabled for cppTango. The suggestions are a lot better for C++ than they are for Python but I think we could work with that, too.

What do you think?