Created by: tpatejko

This PR implements fusion of MKLDNN convolution and elementwise add operator.

MKLDNN supports the conv-sum fusion for residual connections in Resnet networks. These two operators are fused into a single MKLDNN convolution primitive where output buffer is initialized with data to which convolution output will be added.

Elementwise add takes as inputs X and Y outputs from two branches of residual connections in Resnet. The IR pass tries to find the pattern conv -> elementwise add, where Y parameter in elementwise add op is a convolution output, and fuse it into a single MKLDNN convolution. After fusion, X parameter is passed to the new convolution op as ResidualData argument.