Drop using namespace std

[mathisloge]

This drops using namespace std; in most of the files (the ones I could compile) and adds const to some places. IMHO it is ok to use in files where only std lib types are included and used, but as soon as boost or any other 3rd-party lib is included, it can lead to double defined declarations (e.g. boost's dynamic_pointer_cast vs std::dynamic_pointer_cast) it then depends on the order of include which might not desirable.

And adds

set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

to enforce the cxx standard.

Two loops are changed to range based loops

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