Separate includes into sections and alphabetize them

Okay, so basically here's the include layout that this game now
consistently uses:

[The "main" header file, if any (e.g. Graphics.h for Graphics.cpp)]
[blank line]
[All system includes, such as tinyxml2/physfs/utfcpp/SDL]
[blank line]
[All project includes, such as Game.h/Entity.h/etc.]

And if applicable, another blank line, and then some special-case
include screwy stuff (take a look at editor.cpp or FileSystemUtils.cpp,
for example, they have ifdefs and defines with their includes).

desktop_version/src/UtilityClass.h

@@ -2,8 +2,8 @@
 #define UTILITYCLASS_H
 
 #include <SDL.h>
-#include <vector>
 #include <string>
+#include <vector>
 
 int ss_toi(std::string _s);