Fix util namespaces to use the project with C++17 applications

[sergeymarkow]

It is ok to use library which is built with newer C++ standart but it will be great to have including headers to keep C++17 standart.

Unfortunatly I need to use Qt5.15 which still use C++17. Moreover I cannot rebuild Qt5.15 with other C++ params I can use already built project ((. I think in some other cases such change can be required.

[COM8]

@sergeymarkow thanks for contributing!
But I always thought this was c++17 and also the standard says so: https://en.cppreference.com/w/cpp/language/namespace.html

Is this a special case where QT5 does not support this?

[COM8]

Closing for no response. Feel free to reopen in case this is still a problem.