Add inter-implentation CoV calculation

[mathieuboudreau]

The dashboard currently only calculated the mean intra-phantom ROI CoVs, but for inter-implementation comparison we need a different calculation.

I quickly drafted this and it needs to be improved and committed to this repo.

The mean inter-site CoV across the spheres within the brain T1 range (spheres 1-5, ~2000ms to ~500ms) are 5.9% for phantom version 1 and 6.0% for phantom version 2.

[mathieuboudreau]

@agahkarakuzu I just noticed that my past self was very responsible and documented what he did to fix the COV re: our discussion about your Dashboard. Tagged you here for notification =)