Converting to and from cuda-convnet

Unfinished, but creating PR to start discussion.

I plan on creating a tool to convert between cuda-convnet (pickled) files and caffe protobuffers.

At the moment it can (try to) convert the cuda-convnet "schema" to prototxt format (ie., ignoring the blobs). Next I will copy the blobs too and work on going the other way. It also doesn't do anything sensible about the input and loss layers yet.

I you have the supplied decaf net (trained with cuda-convnet) you can try:
```
cudaconv_to_prototxt('./imagenet.decafnet.epoch90')
```