Enable access to `?hash` param

[vinliao]

I found a helpful Discord post by Mark Knol:

Perhaps the code in the first paragraph should be the default. (It's already the default in the Webpack boilerplate...)

It involves a small change:
var fxhash = "oo" + Array(49).fill(0).map(_ => alphabet[(Math.random() * alphabet.length) | 0]).join('');

to

var fxhash = new URLSearchParams(window.location.search).get("hash") ?? "oo" + Array(49).fill(0).map(_ => alphabet[(Math.random() * alphabet.length) | 0]).join('')

And that'll enable things like http://localhost:8080/?hash=oo8NXj8zdYBzETAyPLRj2RxaEqMJHbZf9TLqaCXiFpRyyuHbyq1.

[iuriguilherme]

The webpack boilerplate is already doing it: https://github.com/fxhash/fxhash-webpack-boilerplate/blob/0000e17986e23496cecd813cbfd0c3b0c69c252f/public/index.html#L10