beginners/components: Update and add missing images
Adds missing images that the tutorial linked to and updates the rest. Adds another image that wasn't there at all. Replaces the header image of a text button with a gallery of all shown buttons. Updates and cleans the .ui definitions and adapts surrounding text accordingly. Uses new Adwaita style, includes both light and dark variants.
Resolves #54 (closed)
Edited by Maksym Hazevych