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.

If you have the supplied decaf net (trained with cuda-convnet) you can try:
```
print cudaconv_to_prototxt('./imagenet.decafnet.epoch90')
```