feat: Add new Geometry Nodes groups for image relief and shadeless shader

- Implemented the "O Image Relief Plane" Geometry Nodes group to create a fixed-base image relief using depth images and various parameters.
- Created the "O Shadeless" shader node group to display color without scene lighting while preserving shadows and reflections.
- Introduced a preview feature for node groups, allowing for interactive visualization of node arrangements in an HTML format.
- Added a template HTML file for rendering node previews with customizable views and controls.

tests/test_image_menu.py

@@ -45,6 +45,7 @@ class ImageMenuTest(BlenderTestCase):
             [
                 ("anyimage.convert_to_plane", True),
                 ("anyimage.convert_to_depth_plane", True),
+                ("anyimage.convert_to_relief_plane", True),
                 ("separator", True),
                 ("anyimage.remove_image_background", True),
                 ("anyimage.upscale_image", True),
@@ -101,6 +102,7 @@ class ImageMenuTest(BlenderTestCase):
         )
         operators = (
             (self.convert_to_plane, self.convert_to_plane.ConvertToDepthPlane),
+            (self.convert_to_plane, self.convert_to_plane.ConvertToReliefPlane),
             (self.remove_background, self.remove_background.RemoveImageBackground),
         )