Allow setting padding on DataGrid cells

[KirillOsenkov]

WPF is amazing but there is still a number of scenarios where it feels unfinished.

Please make it very easy to add padding to DataGrid cells. It is possible to work around but it's a bit cumbersome.

Examples:
https://stackoverflow.com/questions/5246745/set-a-padding-on-datagridcells-in-wpf

I suppose it could be a property like DefaultCellPadding of type Thickness on DataGrid itself, and a matching property on each column, which would override the DataGrid one.