DDSXML11 — Incomplete dds-xml_application_definitions_nonamespace.xsd -- allow applications to extend other applications

The specification does not allow <application> elements to extend other already-defined <application> elements. This is inconsistent with what is supported in other elements like <domain_participant> which in fact can be defined to extend other <domain_participant> elements.

The DDS-XML specification, specifically the dds-xml_application_definitions_nonamespace.xsd schema should be updated to support this.