Session replays are not reproducible accross different locale variables

Some parts of Visidata are sensible to the locale variables (LC_*), and some parts of Python are too. Therefore if you capture a session that includes some of that, like converting to a type-float-locale and try to replace the session on a different machine with a different locale set, it will fail or maybe give you the wrong answer.

Suggested fix:

1. We could add a set-env-var command
2. We could use said command set the LC_* variables at the set of the replay

The downside is that every replay would be longer since it would now start with a few variables being set.