fix typo in Handsontable.editors.DropdownEditod
don't overwrite renderer (so that autocomplete cell can actually use a custom renderer from the configuration)
if the value is undefined then it means we don't want to set the value
change the link in the error description
native scroll: DRY the `makeClone` method; move event listeners to a new method `registerListeners`; remove redundant `cloneFrom` checks
move  `getScrollbarWidth` to WalkontableDom
make sure that we not only check if a property is own, but also if it is not empty (setting it to undefined or null should result in a prototype look up)
fix positioning of native scroll elements when one scrollbar is window and another scrollbar is hidden; make code more DRY; this is not a final optimization so review this code in future