Add timezone option

[wolfpackmars2]

Add a timezone option to configure per-user timezone settings.

Thoughts?

[perlchild]

That's an environment variable, and per shell
Wouldn't managing the dotrc of choice do this perfectly?

[noelmcloughlin]

The manpage for adduser does not handle TZ so @perlchild is correct in saying use an environment variable.

By the way, this formula already supports per-user .bashrc so if you are using bash maybe that will work. Otherwise we need a PR.