Migrate to pyproject.toml and reorder files

[elisiariocouto]

Manage this project with Poetry (https://python-poetry.org), reorder files, and reformat with black.

[rveachkc]

Few thoughts:

• I'd prefer you to submit pulls into the adaptive-cards branch, so I've modified this as such.
• I don't want the circleci file deleted until an appropriate alternative system is running in parallel.
• While I can appreciate the migration to poetry, I've already begun using pipenv. I've already committed a Pipfile, but have held off on committing a Pipfile.lock. I really like that it can be apt installed on top of the python docker images (or I'd trust this one: https://hub.docker.com/r/kennethreitz/pipenv). I see that poetry allows you to specify a range of python interpreters. Pipenv doesn't do quite the same, but you can specify a "3", which could work.
• This also appears to lose the version check
• I'm not sure what's going on with the formatting, but I feel like formatting should be a separate pull to make validation easier.

[elisiariocouto]

About your suggestions:

• I will adapt my changes to the adaptive-cards branch.
• The PR was in Draft mode because I still need to migrate from Circle to GH Actions.
• About Poetry vs Pipenv, I really think that Poetry is a better tool. I missed the Python version check, but it's a matter of adding that to the pyproject.toml file. All the packaging and stuff is done automatically with Poetry and we get extra features that are very useful like version bumping. And you can still install Poetry in any python Docker image (pip install poetry).
• I can make the changes in "blocks", to make it easier to review. I will close this PR and open a new one with just the formatting.