Add code quality checks to core projects

[ylep]

Add flake8 checks, Travis tests, possibly protect master branches.

• [x] casa-distro
• [x] brainvisa-cmake
• [x] soma-base
• [x] soma-workflow
• [x] capsul
• [ ] axon
• [ ] aims-free
• [ ] aims-gpl
• [ ] anatomist-free
• [ ] anatomist-gpl
• [ ] morphologist
• [ ] morphologist-ui
• [ ] morpho-deepsulci

[sapetnioc]

I think we should close this issue. We can make a corresponding issue in each project when there is a chance that tests are added.