Make the tables within the html manual easier to read by highlighting on mouseover

[k-doering-NOAA]

This is done for the nav bar: https://github.com/nmfs-stock-synthesis/doc/blob/6dd4560cf6df5686afd488db2adc492316252398/docs/html_usermanual.css#L19

It would also be useful to add this feature for the tables, so the user can more easily read the row of a table.