Fixes for missing fields 

When a page on the Property Tax Portal is missing a field, the scraper fails on that PIN. This code checks for empty values on one webpage fields ("msgPropertyClassDescription") as well as a tax_code_year that doesn't match any of the years that were billed. For example, there are 5 years billed, 2009-2013, but some of the PINs have a tax_code_year of 2008. Python will throw an error because you are trying to add to a key in OrderedDict that doesn't exist.