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/Entity.h

@@ -1,14 +1,14 @@
 #ifndef ENTITY_H
 #define ENTITY_H
 
+#include <string>
+#include <vector>
+
 #include "Maths.h"
 #include "Ent.h"
 #include "BlockV.h"
 #include "Game.h"
 
-#include <vector>
-#include <string>
-
 #define removeentity_iter(index) { if (obj.removeentity(index)) index--; }
 #define removeblock_iter(index) { obj.removeblock(index); index--; }