Persist autoplay

[bradenhilton]

Closes https://github.com/Invertex/Gfycat-AutoHD/issues/6

Tested with:

• Firefox: Violentmonkey, Tampermonkey, Greasemonkey (persistence works, HD seems to be bugged)
• Google Chrome: Violentmonkey, Tampermonkey

I have more fixes and improvements ready but they are outside the scope of this feature, so I think they should be done separately.

Would you be against applying some kind of formatter such as Prettier?

Feel free to make or request changes.

[Invertex]

Thanks for switching the autoplay over to the prefs system.

You can use a formatter on it, though I will say I have a preference for matching braces on same indent depth when possible.