Add object detection related layers for model zoo and keras support (#2015)
Add object detection related layers for model zoo and keras support (#2015)

* Add object detection model zoo support

* Add unit test

* Add more doc and python wrapper

* revert some and add createProposal

* Fix ut

intel-analytics/BigDL,intel-analytics/BigDL,yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL,yangw1234/BigDL,yangw1234/BigDL,intel-analytics/BigDL