Don’t use default focus style it’s ugly.

Don’t allow the image to be dragged.

* removed commented out cruft
* added tabIndex prop to delete button (with default=0)
* the last change also required a change to the sprite selector test snapshot

Prototype of larger delete button for sprites, costumes and sounds to better support touch devices.

I split it out from `CloseButton` as it made the changes simpler, and we may end up going in a different direction (open context menu).