Issue #377: DataGrid Style

I've created a style for the DataGrid. The screenshot shows highlighted row styles, with "Ace of Spades" being the current selected cell, and "A Matter of Life and Death" being the current mouse over cell.

![mahapps metro datagrid](https://f.cloud.github.com/assets/4315787/465850/4085b6ca-b646-11e2-8562-32dedec2f177.png)