Add missing #includes to header files

- Multiple header files where missing #includes to other headers that
  where used in the header. Correct header was included in correct
  order in source files which caused everything to compile.
- Added missing #includes so header files correctly include all their
  dependencies and fixes problems with IDEs being unable to parse
  headers correctly due to missing symbols

Utilities/AtomicPtr.h

@@ -2,6 +2,7 @@
 
 #include "Atomic.h"
 #include <memory>
+#include <cstddef>
 
 // Unfinished. Only std::default_delete will work as expected.
 template<typename T, typename D>