Replace Geotools GeoJSON with thirdpartyutils codec in soql-reference

Happy side effect of removing the reference to geotools-geojson: soql-reference now pulls in about 40% fewer dependency jars :smiley: 
Did a bit of rearranging here but basically I removed 
 "org.geotools" % "gt-geojson" % "11.0"
Replaced it with
"com.vividsolutions"  % "jts"                      % "1.13"
And added
"com.socrata"        %% "socrata-thirdparty-utils" % "2.6.2"