VGG models support

This pull request adds the support for the models described in the BMVC-2014 paper "Return of the Devil in the Details: Delving Deep into Convolutional Nets", K. Chatfield, K. Simonyan, A. Vedaldi, A. Zisserman. This comes down to adding a parameter to the LRN layer, denoted as "k" in [Krizhevsky et al., NIPS 2012].

The models have been converted to the current BVLC caffe format and can be accessed from https://gist.github.com/ksimonyan/5c9129cfb8f0359eaf67 (the link will be added to the Zoo later). The mean image can also be downloaded from the link above.

An important thing to note is that currently the models expect an RGB input, rather than BGR.

An example of how to use the models can be found in matlab/caffe/matcaffe_demo_vgg.m