Display helpful message on orientation modal when Portrait Orientation Lock is engaged

Description:

If a user has Portrait Orientation Lock ¹ enabled (like any sane user does such as myself), we should tell the user. The first time we added this back in November/December, I was confused initially because nothing happened when I rotated my phone from portrait to landscape. I just kept seeing "Insert phone into Cardboard holder." Then, doy! I realised I had portrait orientation lock on, and since we only hide that message when an orientationchange event fires (which never would with portrait orientation lock on), nothing happened. FWIW, the webvr-polyfill has the same problem.

Also, FWIW, I know I'm not alone. I've seen two other people encounter the same problem as I did. I do realise not everyone has portrait orientation lock on, but let's give a good experience. Otherwise, folks will just leave the site if it seems broken.

Anyway, we can easily solve the potential user confusion in this case. Using deviceorientation events, if we detect the user turned the phone landscape on iOS (or any mobile browser where the Fullscreen API is not supported) but no orientationchange event has fired, then let's add a small message below Insert phone into Cardboard holder that says Disable Portrait Orientation Lock.

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- A-Frame Version: `0.1.2`, `master` - Platform/Device: iOS/Android