Currently, all groups are expanded by default. We should expose methods to collapse/expand certain groups. Furthermore, CollapseAll, ExpandAll groups should be considered as well.

Allow binding of complex objects to RadDataGrid.

The DataGrid  documentation is missing a Styling article. It should cover how to use the following:

- DataGridBorderStyle (and how it's used for the RowBackground styles and SelectedStyle
- DataGridTextCellStyle (especially how as the CellContentStyle it lets you set the SelectedTextColor)
- DataGridLoadOnDemandStyle
- DataGridColumnHeaderStyle
- DataGridGroupHeaderStyle
- DataGridHeaderStyle

I think the Styling section might need it's own node with a few articles as the information would be too large for one article