[test] improve windmill integration, new test on relation edition Changes: - display traceback in case of failure - add new use test for relation edition - edition mode is now possible by toggling `edit_test` or with using "pytest -i" - install firebug extension in edition mode - update documentation

include *.py
include */*.py
recursive-include data external_resources *.gif *.png *.css *.ico *.js
recursive-include i18n *.pot *.po
recursive-include wdoc *