Adding VOCdevkit

VOCdevkit used to train DPM model from
http://pascallin.ecs.soton.ac.uk/challenges/VOC/voc2012/VOCdevkit_18-May-2011.tar

Ref:
http://groups.csail.mit.edu/vision/SUN/releases/instruction_VOC2012_DPMv5_SUN2012.txt