add 508 compliance

This goes a long way toward making bonnie 508 compliant.

One open question is tab order; there are a few places where buttons appear to the left of the currently focused button (the "gear" button on the measure page, or the "show delete" button in the data criteria section on the patient builder). I'm not sure how much of an issue that might be, and there might be multiple ways to handle that if it is an issue.