Update to jflow.min.js and jflow.min.css

- The method to minify jflow's sources to jflow.min.js
(https://github.com/mishoo/UglifyJS2) was to advanced, and generated
errors in the code. We went back below the version 3, to avoid the
script being broken when minified.

- The JQuery request 'get_user_files' was bugged because it was trying
to reach ng6-test without the port '8080'.
More information in this jflow commit:
jflow@5c505644

issue #171