Move shader code to external files rather than embedded

A bit of CMake code in each example copies the files to the
correct location and Qt loads them from the application's binary
directory.

examples/common/example.frag

@@ -0,0 +1,19 @@
+#version 130
+
+// Passed in from the vertex shader
+in vec4 worldPosition;
+in vec4 worldNormal;
+
+// the color that gets written to the display
+out vec4 outputColor;
+
+void main()
+{
+	// Again, for the purposes of these examples we cannot be sure that per-vertex normals are provided. A sensible fallback 
+	// is to use this little trick to compute per-fragment flat-shaded normals from the world positions using derivative operations.
+	vec3 normal = normalize(cross(dFdy(worldPosition.xyz), dFdx(worldPosition.xyz)));
+	
+	// We are just using the normal as the output color, and making it lighter so it looks a bit nicer. 
+	// Obviously a real shader would also do texuring, lighting, or whatever is required for the application.
+	outputColor = vec4(abs(normal) * 0.5 + vec3(0.5, 0.5, 0.5), 1.0);
+}