Add support for dilated convolutions

[anibali]

I'm not sure if this is something that you want, but I figured I may as well put up a PR in case someone else wants to do something similar.

• Updated caffe.proto, which involved changing loadcaffe.cpp a bit to cater for some fields which are now repeated. This update was necessary as the dilation field was not present in the outdated caffe.proto.
• Added support for dilated convolutions. When dilation is > 1 for a "Convolution" layer, produce an nn.SpatialDilatedConvolution instead of a SpatialConvolution.