Do not support DataParallel

[HryMurph]

The project has not supported DataParallel and multi GPUs yet. I tried to add the codes myself but found several bugs while running the new version.

1. Line 106, layers.py: edge = torch.cat((edge[:, :], edge_list_nhop[:, :]), dim=1). The shape of parameter 'edge' is (2, n) in the original code. While with DataParallel, the shape of 'edge' becomes (1, n) after a scatter function in DataParallel. Then this line causes Error because the shape of edge and edge_list_nhop in dimmension 1 is different (1 vs 2). The solution to fix it is to transpose the Corpus.train_adj_matrix[0] when initializing Corpus, and then in forward function of class SpKBGATModified, transpose parameter 'adj' again.
2. RuntimeError: Expected all tensors to be on the same device, but found at least two devices. This error raised at Line 114, layers.py: edge_m = self.a.mm(edge_h). However, I have no idea how to fix this error. Hope someone to provide solution.