CMake FetchContent support

Eible library can be now used using FetchContent module in CMake. Added Github workflows for building and testing on Linux and Windows. Added Sonar analysis and Codecov coverage reporting. Added CodeQL analysis. Cleaning majority of Sonar, Clazy and Clang-tidy problems.

First Qt 6 version

First version supporting Qt 6. Built and tested with Qt 6.5.2.

Last Qt 5 version

Last version supporting Qt 5 (build and tested with 5.15.2).