A button column

Could you see if i implemented right the button column?

i used like this:
```
var editColumn = new Backgrid.Column({
    name: "edit",
    cell: Backgrid.ButtonCell.extend({
        title: 'Edit',
        btnClassName: 'btn-danger'
    }),
    label: ''
});

editColumn.on("backgrid:click", function(model) {
    //do ur stuff
});

var grid = new Backgrid.Grid({
    columns: [{
            name: 'some_field',
            cell: 'string',
            label: 'Some Field'
        },
        editColumn
    ],
    collection: urCollection
});
```