cleanup: remove redundant readSettings
move onScroll logic to scrollbar handlers, mark places where it is possible to change the amount of rows rendered before and after table
Revert "cleanup: remove redundant readSettings"

This reverts commit 86e48bab4a3f009b028173945c21398b9e6b89dc.
Partial fix for row offset issues #HOT-12
Distinction between visible and rendered rows updated #HOT-12
refactor: don't use private method of rowStrategy; use public methods instead
refactor: strategy getContainerSize method no longer needs proposedSize argument
refactor: use WalkontableViewportCalculator instead of WalkontableRowStrategy - fix debug overlay
refactor: use WalkontableViewportCalculator instead of WalkontableRowStrategy - add viewportCalculatorOverride to override renderStartRow & renderEndRow
refactor: use WalkontableViewportCalculator instead of WalkontableRowStrategy - remove rowStrategy completely
refactor: use WalkontableViewportCalculator instead of WalkontableRowStrategy - DRY calculation of the number of columns
refactor: use WalkontableViewportCalculator instead of WalkontableRowStrategy - merge WalkontableAbstractStrategy into WalkontableColumnStrategy
refactor: use WalkontableViewportCalculator instead of WalkontableRowStrategy - fix scrolling
refactor: use WalkontableViewportCalculator instead of WalkontableRowStrategy - fix scrolling
fix merge cells when scrolling (#1696, HOT-12)
fix rendering while manual scrolling
bugfix: TD has 'undefined' as class (#1838)
make debugOverlay a little bit more usable
code cleanup (missing semicolons, redundant variables)
cleanup: remove remainings of unused offsetRow (now WalkontableViewportCalculator is used for that purpose)