GPU support for LightGBM wrapper

[mjmckp]

The LightGBM wrapper currently only allows CPU based training, however it is possible to build an instance of the LightGBM dlls which support GPU training..

[Ivanidzo4ka]

DRI RESPONSE: I'm considering to move this to backlog or close it, since it require changes on LightGBM side.

[codemzs]

Please contact Guolin Ke from the light gbm team to have them include GPU Binaries in the nuget. Once they do we can add the option.