Clean up includes

All the headers are now self-contained (g++ Header.h -o /dev/null).

Some system headers where moved to the .cpp they are actually needed in,
some of our own headers are includes less. (Especially MD5.h)

Headers are sorted alphabetically while in e.g. FileUtils.cpp FileUtils.h
is the first file included.


git-svn-id: https://znc.svn.sourceforge.net/svnroot/znc/trunk@915 726aef4b-f618-498e-8847-2d620e286838

String.cpp

@@ -6,10 +6,13 @@
  * by the Free Software Foundation.
  */
 
-#include <string.h>
 #include "String.h"
 #include "FileUtils.h"
 #include "MD5.h"
+#include "Utils.h"
+#include <sstream>
+
+using std::stringstream;
 
 const char* g_szHTMLescapes[256] = {
 	"&#0;", 0, 0, 0, 0, 0, 0, 0, 0, 0,               // 0-9