fixes issue #46

Issue: #46 (closed)

• add course metadata section title
• add question type filter options
• make bloom's cognitive level required in Question UI metadata form
• allow author to add up to 2 topics and 2 curricula references (separately)
• allow editor to link question to other courses
• change structure of resources metadata, and modify component to filter resources for 2 topics
• change QuestionItem view in Dashboard/Discover page; show Learning Objectives and Understandings via a disclosure widget
• memoize Wax editor in Question page to avoid rerendering when parent's state changes;
• refactor metadata flattening functions as utilities
• add utilities for getting random Learning Objectives and Understandings
• prop shape for question list and resources