add an auto-download & import script for the census planning database

[ajdamico]

http://www.census.gov/research/data/planning_database/2016/

The 2016 PDB is a database of U.S. housing, demographic, socioeconomic and operational statistics based on select 2010 Decennial Census and select 2010-2014 5-year American Community Survey (ACS) estimates. Data are provided at both the census block group and tract levels of geography. These data can be used for many purposes, including survey field operations planning. New to the 2016 PDB is the number of individuals with one or more disability.