world: added grass and sky

Shaders/SkyShader.gdshader

@@ -0,0 +1,9 @@
+shader_type sky;
+uniform vec3 skyColor : source_color;
+uniform vec3 horizonColor : source_color;
+
+void sky() {
+	float col = clamp(EYEDIR.y / 0.05, 0.0, 1.0);
+	vec3 finalColor = mix(horizonColor,skyColor,col);
+	COLOR = finalColor;
+}