WIP: add in contextsession to inputs and answer tests.

doc/en/Authoring/Variables.md

question.php

stack/answertest/anstest.class.php

stack/answertest/at_general_cas.class.php

stack/answertest/controller.class.php

stack/cas/ast.container.silent.class.php

stack/cas/cassession2.class.php

stack/cas/security-map.json

stack/potentialresponsenode.class.php

stack/potentialresponsetree.class.php

tests/helper.php

tests/potentialresponsenode_test.php

tests/walkthrough_adaptive_test.php