DataSet: fix data counting

[#63474022]

Remove unnecessary counter that wasn't updated correctly,
just call _numberOfPoints().
DataSet: implement "sampleChanged" event

[#63474022]
TableController: listen to "sampleChanged" event, update view

[#63474022]
TableController: extend table only if non-empty value is added

[#63474022]
Tables: implement "showBlankRow" option that allows users to add new rows

[#63474022]