Add initial toolkit code structure

Created by: stefaniapedrazzi

Prepare the repository for partners' contribution and add the toolkit structures.

Tasks:

• add some folders to define the base structure of the toolkit
• add .gitignore file defining global rules
• add automatic GitHub Action tests checking for:
  • pep8 format for python code
  • clang-format for C/C++ code
  • test that each source code file has a Apache2 license
• add initial version of the engine module and adjust it to pass the format tests