This avoids specializing CSingleton<T>::m_instance for each type, and
instead just defines it once in the header. This is allowed by the
standard, multiple definitions are merged in the same way that inline
functions are.
Introduced in 02c24fbf27, this was supposed to make it more resistant to crashes but turned out to generate huge lag on closing settings
Instead, I added manual .Save() after every value change
Abigail