Forward port of 7.0 to 8.0 with last pylint fixes

I pulled https://github.com/OCA/e-commerce/pull/21                                                                                                                                                             
So it includes all the last changes of 7.0 + the pylint fixes.                                                                                                                                                 
                                                                                                                                                                                                           
Also, .travis.yml conflicted so I corrected it.