Example component_gallery: 12 pages showcasing user interface components, new example transform_primitives: showcasing primitives in viewport

I advise every CGE developer to run these 2 new examples today! 🙂

examples/component_gallery is a 12-page demo of possibilities of user interface components in CGE. Run the demo, and browse the pages to see what is possible. Then explore the demo in the editor (open designs data/page_xxx.castle-user-interface) to see how you can do this.

The screenshots from this demo also augment new manual page about user interface.
examples/viewport_and_scenes/transform_primitives shows possibilities of primitives (sphere, cylinder, cone, sphere, plane, box, text) in the viewport.

The screenshot from this demo also improves manual about viewport.