Add grid granularity to avoid frequent updates when typing at the edge

[dimitar-asenov]

When growing a child object positioned using GridLayouter, the grid will be enlarged with every edit, which causes all other items in the grid to be potentially updated and redrawn.

To reduce the frequency of this costly operation, we could introduce a granularity to GridLayouter. It's size could be a multiple of the granularity which will buffer some of the size changes of child elements. To simplify the API the granularity could be determined based on the space between columns/rows.