Improve pinned requirements (otindex deps only)
Improve pinned requirements (otindex deps only)

This version of `requirements.txt` clearly separates top-level from
lower-level dependencies, and ignores packages introduced by peyotl and
dev tools. This is better for fool-proof deployment, assuming you follow
a similar practice for peyotl in this venv.

To update this file, use

```sh
$VENV/bin/pip freeze –r requirements.in > requirements.txt
```

OpenTreeOfLife/otindex,OpenTreeOfLife/otindex