Add feature to group rows with ability to show aggregate values

[markposterone]

This feature should be able to group rows live (in the run time), end user should be able to choose any column and group rows by the content of that column. Grouped rows should have aggregation rows on the end of the group that can show aggregates of rows in the group (total cost of all items, average price etc). This is one of the examples of implementation: http://examples.sencha.com/gxt/examples/#ExamplePlace:grid_livegroupsummary

[vegegoku]

Added the grouping feature as a plugin, the aggregation feature will added later.

[vegegoku]

Columns groups added https://dominokit.com/solutions/domino-ui/v2/docs/data-table/column-groups SummaryPlugin have been added https://dominokit.com/solutions/domino-ui/v2/docs/data-table/summary