noteweb: Rendering bird field notes for the Web

See Section 10.11, “YEAR_GROUP_FREQUENCY” for an explanation of year groups. This value is the CSS stylesheet class to be applied to year rows that are a multiple of YEAR_GROUP_FREQUENCY. This class name is tied to the CSS rule in Section 5.5, “CSS rules for rows of the index table”.

YEAR_GROUP_CLASS  =  'year-group'