Export answers of -1, -2, etc. as MDES-coded dates / times (PBS)

This addresses https://code.bioinformatics.northwestern.edu/issues/issues/show/4379.

Previously, the instrument warehouse code passed answers of -1, -2, etc. straight through to the MDES warehouse.  In places where dates or times were expected, this caused a format validation failure.

This PR codes -x as 9xxx-9x-9x (for dates) and 9x:9x (for times), using the "9-followed-by-the-code" notation described in the MDES spreadsheets.  Currently, it does so by first trying the value as-is.  If that's valid, we accept it.   Otherwise, we generate possibilities based on the validation format and try those.

This PR is for `1.7.0.pbs`. The main `develop` branch needs this as well; that PR is tracked as #232.