Save caption state in localStorage

[alethea]

As mentioned in #311, captions aren't stored in between page loads. This is an attempt to refactor localStorage usage to accommodate saving captions on/off state when the user hits the captions button.

[sampotts]

Hey, thanks for this. I was just looking through though and thinking it might be best to keep all the settings under a plyr key in the storage and JSON.stringify() and JSON.parse() an object. We'll be adding more to the storage as time goes on and it'd be good to keep them tidy.

[alethea]

That sounds good to me. I was thinking of doing that in this PR anyways but I didn't want to make a big change if that wasn't the direction you were going. I'll refactor this tonight.

[alethea]

I rebased my branch to pull in the latest changes and reworked my implementation to use a JSON store inside localStorage. I chose to make the key captionsEnabled to allow for future language selection or something under a different captions key.

[sampotts]

This looks spot on - nice work 👍

I'm just in the middle of upgrading the Vimeo API but will merge this with that and release today or tomorrow.

Thanks!

[alethea]

Awesome! Thanks so much!

[sampotts]

Hey, thanks for this - I've manually merged this into some other refactoring work I've been doing. 👍