Issue #54:

- {quiz_node_relationship}.child_nid => {quiz_node_relationship}.question_nid
- {quiz_node_relationship}.child_vid => {quiz_node_relationship}.question_vid
Issue #54:

- {quiz_node_relationship}.qnr_id => {quiz_node_relationship}.qr_id
- {quiz_node_relationship}.qnr_id => {quiz_node_relationship}.qr_id
Issue #54: Add description for quiz_relationship.qr_pid column.