Allow KFDataTableViewController subclasses to disable row editing

[calvincestari]

This enables a simple KFDataTableViewController subclass to disable row editing without needing to subclass KFDataTableViewDataSource only to override one method.

[kylef]

I think it's better to do this in UITableViewDelegate as this provides more control over the editing types and allow more control with selective deletion.

- (UITableViewCellEditingStyle)tableView:(UITableView *)tableView editingStyleForRowAtIndexPath:(NSIndexPath *)indexPath {
    return UITableViewCellEditingStyleNone;
}

The data source supports deletion and it should be disabled at the presentation layer.

[calvincestari]

I don't agree. Returning UITableViewCellEditingStyleNone is simply a side-effect of the implementation.

tableView:canEditRowAtIndexPath: defines whether it's possible and tableView:commitEditingStyle:forRowAtIndexPath: defines the result.