Hide "new" button on folderish documents when no sub types

A common problem when configuring the "new" document is that when the current container does not define avec sub types, hitting the button "new" will have no effect (and produce a javascript error)

=> add a filter condition like the default "new" action on Nuxeo and produce a validation error when user explicitely wanted the "new" button to be available but defined no sub types for this document (see NXS-1277)