Set default value for numeric inputs to 0.0 for rows added by the 'Add Row' button.
New javsacript code to propagate date changes to following rows in crop event table.
- Date update wasn't properly updating the 'before' value for the date
  being changed by the user.  This resulted in some odd behavior.
- When Season Start Date is changed, move back any event date that
  now occurs before the season start date.
- TODO: Propogating the changes from Season Start Date to events that
  follow ones that are now too soon is not working. See line 49.