Destroy method should reset changes

Enabling Panzoom and then calling destroy() leaves a bunch of artifacts like cursor:move on the image, overflow:hidden on the parent, etc. Those changes should be undone after Panzoom is removed.

[timmywil]

Ok, rather than changing the behavior of destroy, which would technically be a breaking change and warrant a major version release, I added a new method for resetting all of these styles.

const panzoom = Panzoom(elem)
// ...
panzoom.destroy()
panzoom.resetStyle()

[timmywil]

I think this is generally how styles set by libraries are reverted. The value can then go back to whatever is set in CSS files or browser defaults. Note that getting computed styles can have side-effects like reflows, which can cause flashes. I could just check the style attribute, but saving all that is a good chunk of code. If you have a style you’d like it to be that isn’t the browser default, just set it in your CSS file rather than in the style attribute.