Restructering the repo

[PicoCentauri]

Fixes #200

TODO

• add standalone scripts
• move unit and regression tests into tox workflow
• Build documentation based on tox -e docs
• Add github workflows for tests, lint etc.
• Build per PR docs based on read the docs
• Add codecov token
• Add developer docs for tox workflows

[comcon1]

Current solution.

• ToyData is moved to src/DatabankLib/data
• init.py complains if data folders are set up in the same place where the package folder is located
• user is supposed to run nml_initialize_data [toy/stable/dev] and then if toy - it copies from package data, if stable - copies from stable tag of BilayerData repo (if no git - it downloads and unpack release's zip), if dev - git is required, just simple clone is runned.
• import DatabankLib complains when there is no dir set up EXCEPT being invoked from nml_initialize_data
• test runs from tox first copy ToyData to test and then run tests

I'm satisfied with it. But any comments are welcome @PicoCentauri @MagnusSletten @batukav.

[comcon1]

Ok. Now we passed the tests. I will also take care about documentation a bit before we are done.

[comcon1]

I added what I wanted. During my committing, I was inspecting all the changes, so I have already done a kind of review job here on your parts of code. Let's inspect the code added by me then, and we can merge.

[MagnusSletten]

Looks good! We can make a quick change to the small comments that are the wrong language, maybe we fix the init for windows later.

[MagnusSletten]

This is OS dependent, but maybe we expand to windows in separate PR? Not sure how many besides me use windows on the team. It's not a big change anyways.