* Use horizontalAdvance
* Remove unused code
* Hide some warnings from Qt code
* Remove message for _SILENCE_TR1_NAMESPACE_DEPRECATION_WARNING
* Use CMP0077 NEW
* Move roff libraries to folder Thirdparty
* avoid operator()==
* Remove cmake_minimum_required and set version to 3.15
Enable c++20 in top level cmake. Keep c++17 for GrpcInterface, as the protoc tool does not work with c++20.
Several code adjustments to fix compiler issues.