Switch back to png - jpegs are getting cropped in IE.

For whatever reason, IE crops the jpeg plots at the bottom, making their
x-axes useless.  I switched from png to jpeg in commit 7c3ed94, but
I think the HTML should be the dominant format now. Everyone can learn to use
Paint, for all I care.
For when gender allows multiple selections.

For whatever reason, the Vital Records survey has Gender has three checkboxes
instead of a single multiple-choice question, so it comes through as three
separate Boolean questions.
Add a second pattern of open-ended questions.
Add two new response sets.