Add triangle and quadrilateral tools to the graph tool.

These were requested by Robin Cruz in
https://webwork.maa.org/moodle/mod/forum/discuss.php?d=8646.

The usage of the new tools is documented in the parserGraphTool.pl
macro.

Author: drgrice1

htdocs/js/GraphTool/graphtool.scss

@@ -235,6 +235,14 @@
 			&.gt-sine-wave-tool {
 				background-image: url('images/SineWaveTool.svg');
 			}
+
+			&.gt-triangle-tool {
+				background-image: url('images/Triangle.svg');
+			}
+
+			&.gt-quadrilateral-tool {
+				background-image: url('images/Quadrilateral.svg');
+			}
 		}
 	}