fixed undefined error messages
1. Fixed the bug of the missing covariates/coexposures. This was due to Firefox vs. Chrome issues
2. Revised the "loss to follow-up" text and notes, per Dana's suggestions
3. Changed "exposure assessment notes" to be optional, and swapped location on input form
4. Revised "quantitative exposure level" text, per Dana's suggestions, and also made optional
5. Fixed issue with the "undefined" error messages