Add lazy_gettext
We have some fields that are defined in Mixin or in base Model. The result is that the label and help text are duplicated for each module that inherit from those classes.
This has some negatives impacts like the translations are duplicated in many modules (and there is not check for coherence), the translations table is loaded of many times the same strings. But also it creates a lot of work for the translators when those shared strings are modified like in r e5fdb866f509.
So I would like to introduce a lazy_gettext which is in charge of translating the label/help when used instead of when called.