Add html attachment to cucumber test of import

There is a new validation on publication that prevents publishing
without an attachment. The cucumber test "Scenario: Force publishing a
successful import after speed-tagging" was failing as the data supplied
in the step did not have any attachments.
As discussed with Robin the importer should enforce the same rules as
everything else so imported data will be expected to be valid. As
such the example data has been modified in this patch to included an
html attachment to make it valid.