Add a hidden git sha to home page

[cielf]

Summary

Add a hidden field on the home page that contains the current git sha

Why?

Useful information when it appears a deploy has gone awry.
So that we can be sure that the deployment actually has gone through with what we expect.

Details

Throw it in the footer, please, say, just after HumanEssentials.app. Label "version: " Make sure it's in grey.

It can ask Git, or set an environment variable or put in in a file as part of the deploy.

Criteria for completion

• footer of home page contains the current GIT SHA

Waiting until we move to new environment.