feature: enable multi sell shortcut on inventory

[nolddor]

Closes #263

After implementation a new button will show up on quick sell panel for those items that allow multi-sell being used.
That's when description.commodity is not 0 for that particular asset.

Screenshot

[nolddor]

Hi @xPaw, good day!

Please, take your time to review and provide your feedback.

[nolddor]

Hi @xPaw some comments about this new commit.

1.- As far as I know URLSearchParams does not render as [] even if we use .append instead of .set so I went for items[] as key.

2.- Using encodeURIComponent make the multi-sell to fail as it does not find the item when enconded, so I had to remove that.

[xPaw]

You don't need to encode manually when using that api.

[nolddor]

Then good that I removed it. Thanks for letting me know that, had no idea about it.

[woctezuma]

I had to install Firefox "Extended Support Release" in order to toggle OFF xpinstall.signatures.required. 🙀
After I did that, when I tested the extension on my test profile, the feature worked as intended. 🎉

The result is similar to my usual workflow, except you don't have to Shift-click items, e.g.