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/date_time.h

@@ -1,5 +1,8 @@
 #pragma once
 
+#include <ctime>
+#include <string>
+
 namespace date_time
 {
 	static inline tm get_time(time_t* _time)