support for scrollbars only visible if they are needed 

This build on the patch: https://github.com/angular-ui/ng-grid/pull/1880
When then value is 2 of those new properties it will use the "auto" for the overflow property of the specific scrollbar

Also the scrollbar width/height setting on the grid and container are set to 0 so that the scrollbar is just over the last cell if it is visible and if it is not visible the cell has its full width