Sylvia/docs/api ui text

@stephensanchez @wedaly @Lyla-Fischer Please review and let me know if you have any questions/comments. 

Note: The editor in me doesn't like that we use double quotes around names, etc. in most files but single quotes in the xml.py file (e.g., *The "must_grade" value* vs. *The value for 'points'*), but I didn't feel like going through and making lots of manual changes in xml.py.