Visibility at horizontal flip

Swap also visibility flags [here](https://github.com/ds2268/caffe/blob/master/src/caffe/data_transformer.cpp#L707) as already [here](https://github.com/ds2268/caffe/blob/ski_jump/src/caffe/data_transformer.cpp#L780) or instead use this [fork](https://github.com/ds2268/caffe/tree/ski_jump/src/caffe) that should still work with original COCO dataset and will be merged in the future.