* Created _scroll extension point and migrated scroll code from _mouseDrag
* Cleaned up logic for scrolled
* Fixed appendTo functionality to match documentation
* Remove unnecessary function calls
* Move set-up position functions to appropriate place
* Base scrollParent on placeholder and not helper
* Update scrollParent when switching containers
Fixes#3173Fixes#15165Fixes#15166Fixes#15167Fixes#15168Fixes#15169Fixes#15170
Closes gh-1793
The sortable was using the window position compared with page position to
determine where to drop objects. this was only a problem for sortables far
enough down to require scrolling.
Fixes#10727Fixes#5039
Closes gh-1475
Closes gh-1585
