The changes in this commit revolve mainly around overhauling the geoID
fields for census tracts. They were previously stored as longs, but this
would trim the leading zeroes which are part of the geoID's identities.
Made an immutable object to track them instead.

CensusTract: Changed GeoID field to new implementation and added
boundaries as a field.

CensusTractParser: Added function to parse GeoID fields into the new
GeoID objects.

CensusTractParserTest: Updated test to reflect GeoID objects instead of
prev. long values.

Tract_Data: Deleted MD tract data in favor of using national tract data
file (get 'em all at once.)

GeoID: The GeoID object - tracks 3 independent fields of a GeoID.

ParsingService: Bundles up both the KML and the tract data parsers to
provide unified access.