Moving more source code, now all looks tidy

src/core/_SourceFiles.cmake

src/core/clock.cpp

src/core/config.cpp

src/core/control.cpp

src/core/core.cpp

src/core/dummy.cpp

src/core/events.cpp

src/core/file_handling.cpp

src/core/finalize.cpp

src/core/homogeneous_medium.cpp

src/core/init.cpp

src/core/initialize.cpp

src/core/locking.cpp

src/core/module.cpp

src/core/object.cpp

src/core/progress.cpp

src/core/rendering.cpp

src/core/reproduction.cpp

src/core/reset.cpp

src/core/scene.cpp