Weights pretrained at Cityscapes dataset

Thanks @rdiazgar for adding Cityscapes weights. To use them just pass weights=cityscapes while initializing the model.

Pretrain on PASCAL VOC train&val sets

Weights for keras models pretrained on PASCAL VOC train&val sets
This files don't have models definition, so you need to load them into existing model with:

deeplab_model.load_weights('deeplabv3_xception_tf_dim_ordering_tf_kernels.h5', by_name = True)