Add support for Upsample op in CAFFE

[gasgallo]

Currently it's possible to simulate UpSample op in CAFFE using a deconvolution layer, but this supports only a bilinear kind of resizing of the image. Instead we can implement a real UpSample op with nearest neighbor algorithm and exploit the fact that nearest neighbor algorithm is already implemented in MACE (but not properly wired).

Using resize_nearest_neighbor instead of deconvolution improves image upsampling speed by 2-4x in my tests.