add include_triggers parameter to XForm.get_questions()

and move excluding triggers in app builder case management into
case-config-ui-2.js in preparation for case reference display in
case-config-ui-2.js needing to have access to all questions, including
triggers.
add tests for XForm.get_questions()
Merge pull request #1917 from dimagi/get-questions

add tests for XForm.get_questions()