v0.3.1: created new module ae.system, migrated from ae.base

A  .gitignore
A  .gitlab-ci.yml
A  CONTRIBUTING.rst
A  LICENSE.md
A  README.md
A  SECURITY.md
A  ae/system.py
A  dev_requirements.txt
A  pyproject.toml
A  requirements.txt
A  setup.py
A  tests/conftest.py
A  tests/requirements.txt
A  tests/test_system.py