rename WalkontableScrollbarNative to WalkontableOverlay
remove unused properties and methods
get rid of lint warning
rename WalkontableScrollbarNative to WalkontableOverlay (2 places ommited by unintentionally)
two Walkontable tests were failing after a recent change [reuse original columnStrategy/rowStrategy in clones]
fix misleading name of a method
what seemed to be a quick fix but was not - column headers in native scroll were not streched when data source had 0 rows
oops those errors cannot be thrown there
move native scroll viewport with keyboard horizontally
refactor cloneDirection (string) to cloneOverlay (object)
rename cloneFrom to cloneSource
Merge branch 'feature/bugfix#1149' into develop
Merge branch 'feature/bugfix#1198' into develop

Conflicts:
	src/3rdparty/walkontable/src/scrollbarNativeHorizontal.js
	src/3rdparty/walkontable/src/scrollbarNativeVertical.js
	test/jasmine/spec/plugins/columnSortingSpec.js
Merge branch 'feature/bugfix-#1124' into develop

Conflicts:
	src/3rdparty/walkontable/src/cellStrategy.js
	src/3rdparty/walkontable/test/jasmine/spec/rowStrategy.spec.js
Merge branch 'feature/bugfix-#1084' into develop
Merge branch 'feature/selectEditorNotExpanding' into develop
Merge branch 'feature/bugfix-#1199' into develop
Merge branch 'feature/htmlRenderer' into develop
Merge branch 'feature/copyPastePlugin' into develop
Merge branch 'feature/cancelEditValidation' into develop