A-Frame Showcase needs updating

Tracking as an issue intially - will follow with a PR when scope is clear.

Showcase has not been maintained in years, has a load of broken links, and doesn't link to a range of more recent projects that show what A-Frame can do.

Goal is to:

• remove broken links
• add some examples of current sites that use A-Frame
• as a by-product, make this an attractive place for new A-Frame projects to be listed, which should help to better maintain the showcase going forwards.

Need to compile 2 lists:

• Existing links that are dead & should be removed (unless the target is expected to be revived soon, e..g. A-Painterm in which case they should stay)
• New links that we should add. I can poll on the WebXR discord aframe channel to see what peope suggest should be linked to, as up-to-date exampls of what A-Frame can do.

Existing Links

...to complete...

New links

...to complete...

Start with the A-Frame showcase referenced in this issue and review its existing links, then compile the dead-link and new-project lists. Use the WebXR Discord aframe channel for suggested current examples, and consider the work done when broken links are resolved or removed and suitable current A-Frame sites are added.