HiFaceGAN integration. (#395)

* 20210523: [Lotayou] HiFaceGAN test merge
@ Currently use SRModel as a wrapper, will convert HiFaceGANModel later

* 20210525 [Lotayou]: HiFaceGAN training code merged

* 20210528 [Lotayou]: Migrate HiFaceGAN metric package
Note: Currently this commit is non-intrusive by hosting another registry
METRIC_REGISTRY_LOTAYOU

* 20210616 [Lotayou]: Suspend metrics_Lotayou and return to default;
Minor syntax and format changes. Ready for merge.

* 20210718: Minor format change & comment deletion

Co-authored-by: whduan <whduan@sjtu.edu.com>
Co-authored-by: Lotayou <lotayou@163.com>