The date picker itself is a view controller inside of a UIPopoverController that we display when the user double taps on a custom cell.
The "Add New..." button you see in Shinobi play doesn't really have anything to do with the grid or it's datasource. All that we do there is update the bottom content inset on the scroll view that the grid is contained in, and add a UIButton as a subview of the grid.
Unfortunately the code for ShinobiPlay isn't available to the public, but we do have a lot of blog posts on how to customise our grids and charts available in our blog section of the site.
Hope that helps!