Fix: Add ZF Net model to FabrikZoo(#105)

[prakharchoudhary]

@utsavgarg In reference to issue #105 I found ZF net to be a viable addition to the models. Hence, I am making this PR.

[coveralls]

Coverage remained the same at 96.754% when pulling 15651b1 on prakharchoudhary:ZFnet into d036beb on Cloud-CV:master.

[utsavgarg]

@prakharchoudhary The prototxt does not load in Fabrik. Please test it on fabrik.cloudcv.org before submitting a PR.

[prakharchoudhary]

@utsavgarg I found the prototxt file for ZF net using faster rcnn on the following link:
https://github.com/rbgirshick/py-faster-rcnn/blob/master/models/pascal_voc/ZF/faster_rcnn_end2end/train.prototxt
Can you please have a look as to why this prototxt file is being termed invalid?

[utsavgarg]

@prakharchoudhary It is because that prototxt is using a custom layer SmoothL1Loss which is not part of the standard Caffe package.

[prakharchoudhary]

@utsavgarg SmoothL1Loss is necessary for the fast rcnn based zf net model. So should we wait until Caffe provides support for this layer? Or maybe we can use the fast-rcnn fork of caffe (here at: https://github.com/rbgirshick/caffe-fast-rcnn) in place of the standard version.

[virajprabhu]

@utsavgarg Is SmoothL1Loss not a Python layer?
@prakharchoudhary In general, I don't think switching to third-party Caffe forks to support custom layers is a great idea in the long run. Also, please remember to resolve conflicts before you submit a PR.

[utsavgarg]

@virajprabhu No it's not a Python layer but a custom layer implemented in cpp/cuda.

[coveralls]

Coverage remained the same at 96.754% when pulling e7bab7a on prakharchoudhary:ZFnet into 36d4e5d on Cloud-CV:master.