ISO/IEC 23009-1 MPD schema validation

Validator implements checks to assert conformance to the ISO/IEC 23009-1 xsd (official) schema.

Must Fix 6.2.2a

MPEG-DASH XSD schema validation against the schema available on |dashschema|_ xmlschema is used and text on failures are reported from XMLSchema

Not Supported

DASH MPD with multiple namespaces at the root level, xmlns attributes such as sometimes used for AVS3 are not supported.