Use Files provider feature when Documents not available
As future versions of gnome-online-accounts will have the Documents provider feature disabled1, gnome-documents should use the
Files provider feature instead of
This should allow the Google and NextCloud/OwnCloud providers to carry on working for gnome-documents, but not the Microsoft/Skydrive one.
Note that there is currently nothing in the gnome-online-accounts API that would allow differentiating between Documents being disabled, and Documents support not being compiled in. See gnome-online-accounts#43