Major Browser Extension build must check the whole code style. 
It must checks:
- app/scripts.babel/*.js: ES6
- app/vendor//.js: ES5
Ideally, result must be stored in ftest/target/checkstyle-result.xml; or adapt Jenkinsfile
- It could also be the case to extract a app/vendor.babel/*/*js that will be transpiled to app/vender/ like what is done for scripts. According to the changes, adapt checkstyle to ES6 in vendor folder.
- To check also, if we can avoid to have two separate folders in app (*.babel, and his corresponding transpiled folder); and transpile sources only when building the extension.
-see comments
