Added JqGrid groupingView including example

Fixes issue https://github.com/ThaDafinser/ZfcDatagrid/issues/108

JqGrid `groupingView` example URL:
http://YOUR-PROJECT//zfcDatagrid/jqgrid/groupingview

This PR will not add `groupingView` as a new feature itself. It simply adds an example that shows how to set `groupingView` to an individual layout.

The example is based on the `JqGrid` demo:
http://trirand.com/blog/jqgrid/jqgrid.html - Grouping - Grouping row(s) collapsed

The important part is the `Renderer` that has been changed in order to allow `sorting` when using `groupingView`.