Optframe

- fixed examples
- many small fixes according to v4 concepts philosophy
- added github actions for compilation tests
- added demos on quickstart

- start broad support for examples (some still not compiling)
- improve support for optframe functional core (and start support for fxcore c++20)

- migrate into MIT License model, that corresponds into newer open-source community global standards (from previous LGPLv3 license)
- fix many bugs from v4.1
- large refactor to adopt standard memory management for all components (from *widget&* into *not null shared pointer* "sref")

- explored gcc bug "a variable concept cannot be constrained", meaning that during concepts
definition we cannot replace auto rules (class R) by constrained ones (XRepresentation R)
* Same as: "https://github.com/boostorg/asio/issues/312" => "https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67658"
- Fixing other bug "error: result type is not a plain type-constraint" (when variable concepts are put on return types, e.g., "-> XSolution&")

- Adjusted tests from deprecated [gtestlib](https://github.com/google/googletest) to [catch2](https://github.com/catchorg/Catch2)
- Fixed MCT and examples to standard format (`src/`, `tests/`, `build/`, etc)

- Fixing remote reference to a stable [Scanner](https://github.com/optframe/scannerpp) version.
- Fixing remote reference to deprecated [gtestlib](https://github.com/google/googletest).