Added class GCodeViewer -> basic render of gcode toolpaths using dedicated shaders

resources/shaders/toolchanges.vs

@@ -0,0 +1,15 @@
+#version 110
+
+varying vec3 eye_position;
+varying vec3 eye_normal;
+//// world z component of the normal used to darken the lower side of the toolpaths
+//varying float world_normal_z;
+
+void main()
+{
+    eye_position = (gl_ModelViewMatrix * gl_Vertex).xyz;
+    eye_normal = gl_NormalMatrix * vec3(0.0, 0.0, 1.0);
+//    eye_normal = gl_NormalMatrix * gl_Normal;
+//	world_normal_z = gl_Normal.z;
+    gl_Position = ftransform();
+}