Release ssdlite mobilenet v2 coco trained model, add quantized training and minor fixes.

[pkulzc]

196161788 by Zhichao Lu:

Add eval_on_train_steps parameter.

Since the number of samples in train dataset is usually different to the number of samples in the eval dataset.

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196151742 by Zhichao Lu:

Add an optional random sampling process for SSD meta arch and update mean stddev coder to use default std dev when corresponding tensor is not added to boxlist field.

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196148940 by Zhichao Lu:

Release ssdlite mobilenet v2 coco trained model.

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196058528 by Zhichao Lu:

Apply FPN feature map generation before we add additional layers on top of resnet feature extractor.

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195818367 by Zhichao Lu:

Add support for exporting detection keypoints.

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195745420 by Zhichao Lu:

Introduce include_metrics_per_category option to Object Detection eval_config.

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195734733 by Zhichao Lu:

Rename SSDLite config to be more explicit.

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195717383 by Zhichao Lu:

Add quantized training to object_detection.

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195683542 by Zhichao Lu:

Fix documentation for the interaction of fine_tune_checkpoint_type and load_all_detection_checkpoint_vars interaction.

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195668233 by Zhichao Lu:

Using batch size from params dictionary if present.

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195570173 by Zhichao Lu:

A few fixes to get new estimator API eval to match legacy detection eval binary by (1) plumbing `is_crowd` annotations through to COCO evaluator, (2) setting the `sloppy` flag in tf.contrib.data.parallel_interleave based on whether shuffling is enabled, and (3) saving the original image instead of the resized original image, which allows for small/medium/large mAP metrics to be properly computed.

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195316756 by Zhichao Lu:

Internal change

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PiperOrigin-RevId: 196161788

[jch1]

Thanks Zhichao!