Support for paging heights.
Ensure resize occurs initially.
Adding showAutofitButton property to grid.
Adding autofitIfSpaceAvailable support. This expands columns if there is available space in the grid area.
For auto fit, scrolling position is calculated initially, rather than just when scrolling occurs.
Ensure that multi-select checkbox retains min-width.
Prevent auto sizing going from  non-auto -> auto -> non-auto.
Merge pull request #282 from PrimeRevenue/feature/horizontal_scroll_button

Support for paging heights.