Add "Group by N" module

We routinely have to do grouping when making API calls.  That can be over several thousand objects, grouped into bunches of only 50.  It's inefficient to deal with it using the existing mechanisms, such as aggregating to a list and then doing complex slicing with a Repeater.  It would be much more resource-efficient to have a module that aggregates up to some number "N" into a single output array.