Put dev scripts into their own python module

[almet]

Currently, dangerzone uses standalone dev scripts, living in the dev_scripts and install folders.

We could put these scripts inside a common module, which would make it possible to:

• Factorize some code in utility files.
• Use third-party packages like requests and click.
• Maybe even check them with MyPy, as we do for our regular code.

See the discussions about this:

• here about putting our tooling in a separate python modyle ; and
• here about using third-party libraries rather than stdlib modules like click and requests

[apyrgio]

Thanks for opening this issue Alexis! Just so I don't forget, you asked at some point what's the reason why we don't use third-party dependencies in our dev scripts. I don't have a very strong reason actually. I preferred to keep things simple, since they are dev scripts after all, and wanted to ideally run these scripts in a CI, without having to install Poetry and all the project's packages.

Those are preferences though, not blockers.