Add Insightface ARCFace as a face embedder

[frankier]

This is a tracking issue for different face embeddings. The main criteria what the cropping procedure is (is it compatible with dlib?) are how well it performs on different benchmarks and the size. LFW is compared first since it's the most common.

Name	Dim	LFW acc	Ref
insightface ARCFace	512	99.83	1
FaceNet trained on VGGFace 2	512	99.63	1
vgg-face embedding loss	1024	99.13	1
dlib	128	98.4/99.38	1 2

Better evaluation: https://www.cs.tau.ac.il/~wolf/ytfaces/ (v. relevant here) https://ieeexplore.ieee.org/document/8575544

[frankier]

Looks like Insightface ARCFace is the only one worth adding:

https://github.com/nizhib/pytorch-insightface https://github.com/deepinsight/insightface

Keypoints are here: https://github.com/deepinsight/insightface/blob/5b40f4bfce7e2c9d10bb6328c4fed33e9d76c9de/python-package/insightface/utils/face_align.py#L31

[frankier]

Note that ARCFace probably uses cosine distance, unlike dlib so this needs to be taken account of. (Need to double check this.)