Add tensorflow ssd_mobilenet_v1_coco_2018_01_28_nopp.tgz

[apivovarov]

This tar.gz file contains tflite ssd_mobilenet_v1 file created from official model ssd_mobilenet_v1_coco
https://github.com/tensorflow/models/blob/master/research/object_detection/g3doc/detection_model_zoo.md
Oficial ssd_mobilenet_v1_coco_2018_01_28.tar.gz file contains checkpoint

To create tflite file I did the following

1. The checkpoint was exported to tflite compatible pb file using official export_tflite_ssd_graph.py util
2. pb file was converted to tflite file using tflite_convert util (custom post processing operator TFLite_Detection_PostProcess was not included)
3. tflite file was packed to ssd_mobilenet_v1_coco_2018_01_28_nopp.tgz
4. ssd_mobilenet_v1_coco_2018_01_28_nopp.tgz was added to tensorflow/models/object_detection/ folder in this repo

This tflite file is used in tflite tests in PR apache/tvm#3350

[apivovarov]

@FrozenGene can you have a look?

[FrozenGene]

LGTM. @srkreddy1238 @tqchen could you help to handle it?