stable_backport: support manual backport files for complicated cases
Some weboob core modules should not simply be copied just to backport one symbol. It causes every class to be redefined even if they did not change. Instead, use some manual code backports for some of them. Should close: https://git.weboob.org/weboob/devel/issues/111 https://git.weboob.org/weboob/devel/issues/100