Top-level code environment updates

[soltanoff]

• ~~wxPython 4.2.0 compatibility~~ (https://github.com/venthur/snakerunner/pull/4)
• ~~Fixed deprecation warning~~ (https://github.com/venthur/snakerunner/pull/4)
• Fixed top-level code environment
• Modernized setup.py: updated and fixed installation meta
• Modernized version control: rename version.py -> vertion.txt
• Added requirements.txt
• Added .flake8 and fixed the code
• Added .editorconfig
• Updated application resource

[soltanoff]

@venthur, hi! Might you review this PR?

Thank you!

[venthur]

Hi,

thank you very much for the PR! Can you please separate the wxpython specific changes from the other ones? I.e. there are a lot of unrelated changes in this PR, which should go into separate ones so I can review and merge them individually.

Thank you!

[soltanoff]

Hi,

sure! PR is ready: https://github.com/venthur/snakerunner/pull/4

Thank you!

[soltanoff]

I’ll rebase it soon. Thank you, @venthur!