added missing generic type arguments
Bug 455318 - add support for configuring the ILayer that should be used
to copy cells
corrected creation of the LabelStack in FixedSummarRowLayer to add labels correctly for a row header cell
Bug 455327 - changed GroupByObject#descriptor to the a Map<Integer, Object>
Bug 448115, 449361 - introduced the GroupByDisplayConverter to be able to use correct conversion for GroupByObject values instead of toString()