Adds three new classification modes to graduated symbol renderer (version 2), including Natural Breaks (Jenks), Standard Deviations, and Pretty Breaks (based on pretty from the R statistical environment)

git-svn-id: http://svn.osgeo.org/qgis/trunk/qgis@14308 c8812cc2-4d05-0410-92ff-de0c093fc19c

Author: cfarmer