Fixed bug with Entity and MultiEntity fields storing a "name" field

- A recent commit allowed Entity fields to store a name value if
  the value passed to _fromFieldData contained it.

  This was in response to AppWelcome and Banner Entity types returning
  a field only avaiable when quried from a field belonging to another
  Entity.

  The Entity field classes now only allow AppWelcome and Banner types
  to store the "name" field, before it was allowed for all types.