Thread-safety is guaranteed in C++11.
No more need for a mutex lock.

Minimize code around fixed names

Zero warnings under clang 9.0.1, swig 4.0.1

used script:
    t = re.sub(r'new QString\(("[^"]*?")\)', r'###NEW(\1)', t)
    t = re.sub(r'QString\(("[^"]*?")\)(\s*\+\s*)', r'###ADD(\1)\2', t)
    t = re.sub(r'QString\(("[^"]*?")\)(\s*\.)', r'###ADD(\1)\2', t)
    t = re.sub(r'QString\(("[^"]*?")\)', r'\1', t)
    t = re.sub(r'###NEW\(("[^"]*?")\)', r'new QString(\1)', t)
    t = re.sub(r'###ADD\(("[^"]*?")\)', r'QString(\1)', t)

Replace ThirdParty/Core/Faddeeva by dependence on our libcerf

this requires some ad-hoc code to work with both the C and the CPP
version of libcerf.

CMake: simplification and modernization

Extend them to CMakeLists.txt,
and bundle the checks in one CMake module.

cmake/bornagain/modules -> cmake/modules
cmake/bornagain/scripts -> cmake/configurables
cmake/generic/modules   -> cmake/extensions

CMake: remove options PYTHON2 (never again) and OPENGL (always on)