generalize draft import/export TNL-574

add test for videomodule

Import drafts handles modules w/o xml_attributes
and ones using the old parent_sequential_url pointer

Handle drafts for modules which don't define nor extract xml_attributes

Support  and  in get_items qualifiers

Unit test for   value query
Merge pull request #5538 from edx/adam/generalized-draft-import-export-2

Adam/generalized draft import export 2