Mask R-CNN model added to models/research/mlperf_object_detection/Mask_RCNN (#4678)

* Create README.md

* readme changed

* readme changed

* ResNet backbone completed.

* FPN added

* Create README.md

* initial commit

* files removed

* initial commit

* protobuf file removed

research/mlperf_object_detection/Mask_RCNN/object_detection/data/kitti_label_map.pbtxt

+item {
+  id: 1
+  name: 'car'
+}
+
+item {
+  id: 2
+  name: 'pedestrian'
+}