Consider a good workflow for creating (batou) appenv lock files

[ctheune]

@sweh started an implementation that works for him but isn't obviously the right choice for inclusion within batou.

The original discussion started in #69 and should continue here.

[ctheune]

Pinging @SoerenWeber as he was involved in the discussion in #69

[sweh]

So that some discussion starts here, I would like to throw in pip-tools. Would that be a useful addition to represent the requirements workflow properly?

https://github.com/jazzband/pip-tools

[ctheune]

pip-tools looks definitely interesting for this. The filenames are a little bit different from what we currently use.

Do you know whether they properly support editable and version control dependencies?

[sweh]

Stumbled upon pip constraint files. They could be handy in defining versions for multiple App envs.

https://pip.pypa.io/en/latest/user_guide/#constraints-files