removed trailing whitespace
converted the plot functions to a class template
added docstring to Graph.__init__
added Graph.draw_isolines wrapper function
getIsoLines - removed redundant if and else statements
getIsoLines - removed commented out code
getIsoLines - replaced if-else statements with dictionary mapping
getIsoLines - cleaned up the range generation for the isolines
removed old test code
moved getIsoLines to a class object IsoLines
removed functions _getIsoLineIds and getIsoLineColour - added these dictionaries to the IsoLine class object
cleaned up exception handling
+ removed function _plotXY added to IsoLines.__init__
moved drawIsoLines to class object IsoLines
cleaned up IsoLines.draw_isolines
moved _setBounds to class object IsoLines.__set_axis_limits
moved _getI_YX to class object IsoLine.__get_isolines_data
updated Graph.draw_isolines function to use the IsoLines.draw_isolines function
cleaned up IsoLines.__set_axis_limits code
fixed missing function declaration
cleaned up IsoLines.get_isolines code