helper fixes for patient exports

Conflicts:
	lib/health-data-standards/export/helper/scooped_view_helper.rb
workaround: add code, code_system, and codeSystemName to ordinality
workaround: new xpath for negation reason, and add code_system to negation reason
fix arity of population.population_count in continus variable value cat3 template
ignore blank top level populations in measure section