Clean separation beetween Document.type_info and LanguageRoot.type_info

Hi,

I think there is a problem regarding LanguageRoot.type_info:
it shares references to Document.type_info.selectable_default_views and other Document.type_info's attributes.

Therefore adding a default view to LanguageRoot also adds it to  Docmuent and vice versa, among other things.

That is not what we want right ?

Regards.