* support no label training

* fix load_crowd

* update to fit rbox

* add empty_ratio

* update configs

* support mask rcnn

* clean drop_empty for mot & keypoint

* refine is_crowd

* fix voc eval

* remove debug code

* add comments

* update comment for collate_batch

* add ssd config file, test=kunlun

* revise file format

* unify log_smooth_windows and log_iter

test=develop

* remove duplicate log_iter

* remain mobile yml, since they are soft-link

test=develop

* update mbv3 ssdlite

* fix ssdlite link

* add mobilenet v3 configs

* fix some comment

* fix memsize

* add devices_num on reader

* refine capacity value

* refine bufsize

* add blazeface nas demo

* fix format

* fix configs

* fix reduce_rate

* Polish Reader to simplify preprocessing logic.
#  sample_transforms-> make batch -> batch_transforms in Reader.
* Clean some code
* Imporve yolov3_r50vd_dcn_obj365_pretrained_coco 41.4 to 41.8.
* Update all configs.

* change voc_loader

# Add VGG-SSD on VOC and COCO dataset.
# Add config and model zoo. 
# Refine bbox2out and draw_bbox:
    - Add bbox de-normalize in bbox2out function.
    - Remove bbox de-normalize in draw_bbox.