Pretrained model on Visual Genome?

## 🚀 Feature
I was wondering if pretrained models on the Visual Genome dataset will be released? Right now, all the models in the MODEL_ZOO are trained and evaluated on MS-COCO.

## Motivation & Examples
Many papers have been published where they used Faster-RCNN features extracted from a model trained on Visual Genome. To compare with these publications, it would be good to use a similar pretraining. Since this would be helpful for many researchers so they easily extract comparable features from data, it would be good to add this to detectron2.
Plus it would save a lot of time/energy if not everybody had to train this.

Thanks in advance.