Add default shaders to terrain sample

samples/terrain/terrain/default/default.ps

@@ -0,0 +1,4 @@
+void main(void)
+{
+	gl_FragColor = gl_Color;
+}

samples/terrain/terrain/default/default.vs

@@ -0,0 +1,13 @@
+in vec4 vertex;
+in vec2 coords;
+
+// Model-View-Projection matrix
+uniform mat4 mvp_matrix;
+uniform vec3 color;
+
+void main(void)
+{
+	gl_Position = mvp_matrix * vertex;
+
+	gl_FrontColor = vec4(color, 1.0);
+}