SP2: Refactor the "Apply to all Languages" checkbox + text into a switchable "field icon"

We could gain quite a lot of room, for all fields (not only the big text one), in multilanguage mode, by removing the "Apply to all languages" checkbox.

I suggest to create a "switchable" icon field where, by clicking on the field icon, we could activate recopy the values to other languages or not (for example by creating a copy of all fields icon but with a small chain at the bottom of the field icon).

Ideally it would be great to store such values within the container properties (or the field properties if they exist) so that we could keep the default values for such fields (and avoid reclicking each time on the "apply to all language" icon).