During this refactoring a new approach of padding elements height calculation was developed.

Now the ui.scroll engine remembers the height of all items that were in DOM once. This allows to make a precise computation of scroll parameters. Yellow part of the diagram.

Also if the programmer sets dataset boundaries (via datasource.minIndex and datasource.maxIndex) then we have an additional calculation based on average item height. Cause these items are just potential and have never been in DOM. Green part of the diagram.

It solves Average items height problem.

Also some new examples were added into the demo folder.