conv does not support group argument or channelmajor format

[denizyuret]

I did not find this in other issues, if not elsewhere should add it to our todo list. For a description of grouped convolutions see:
https://towardsdatascience.com/a-comprehensive-introduction-to-different-types-of-convolutions-in-deep-learning-669281e58215

[denizyuret]

Another option used in cudnn is the channelmajor (CUDNN_TENSOR_NHWC) tensor format.

[CarloLucibello]

Only the channelmajor feature left after #289