Proposed changes

As in the old VeganCheck app based on PHP, there should also be a fallback for the share button if navigator.share is undefined.

On v2.x-PHP you can find the old share modal beginning from main.php:72:
https://github.com/JokeNetwork/vegancheck.me/blob/0ed4d268aee694480a81dd8a9a2a1a433ed3119b/main.php#L72-L103

and the correspondent Javascript can be found beginning from app.js:309:
https://github.com/JokeNetwork/vegancheck.me/blob/0ed4d268aee694480a81dd8a9a2a1a433ed3119b/js/app.js#L310-L359

Related issues

This is related to #154.