Add error handling in case the overworld iframe or a minigame iframe fails to load

[robojones]

Description

If any of our iframes fail to load, the user is left with a fullscreen iframe and no way to return to the previous screen.

Proposed Solution

• When page A opens an iframe, it should create the iframe and hide it with CSS.
• When loaded, the page within the iframe should send a window.parent.postMessage('...') to the outside page.
• The outside page waits until it receives the postMessage or a timeout runs out.
• Then the outside page removes the CSS hiding the iframe

DoD

Todo