X3D: Expanding Architectures for Efficient Video Recognition model

Hi,
Thank you for opening your work on SlowFast model to us.
Would you mind updating the video_model_builder.py as well as other layer helper file in order to support for X3D configuration, follow your recent report: https://arxiv.org/pdf/2004.04730.pdf
I am kind of interested in the enhancement of this model, and also trying to reproduce the result on your paper, but it seems something wrong that I may miss from reading your paper, so my self-writing X3D-M model still not get expecting results to be close to SlowFast 8x8-R50 model.
Thank you.