Make R-CNN the Caffe detection example

R-CNN [1] is a state-of-the-art detector powered by a finetuned Caffe model. As an off-the-shelf example, I have made a pure Caffe version of R-CNN, ILSVRC13 detection edition, by

1. making a new model, caffe_rcnn_imagenet_model, with the RCNN class SVMs transplanted a fully-connected layer
2. adding an R-CNN crop mode to the pycaffe `Detector`
3. rewriting our detection example, which runs the Caffe Reference ImageNet Model classifier on selective search windows.

@rbgirshick please review to make sure that everything is clear. Thanks!

1. Rich feature hierarchies for accurate object detection and semantic segmentation. Ross Girshick, Jeff Donahue, Trevor Darrell, Jitendra Malik. CVPR 2014. Arxiv 2013.