util-lib: split our string related calls from util.[ch] into its own file string-util.[ch]

There are more than enough calls doing string manipulations to deserve
its own files, hence do something about it.

This patch also sorts the #include blocks of all files that needed to be
updated, according to the sorting suggestions from CODING_STYLE. Since
pretty much every file needs our string manipulation functions this
effectively means that most files have sorted #include blocks now.

Also touches a few unrelated include files.

src/basic/clock-util.c

@@ -20,13 +20,14 @@
 ***/
 
 #include <errno.h>
-#include <stdio.h>
 #include <fcntl.h>
+#include <linux/rtc.h>
+#include <stdio.h>
 #include <sys/ioctl.h>
 #include <sys/time.h>
-#include <linux/rtc.h>
 
 #include "macro.h"
+#include "string-util.h"
 #include "util.h"
 #include "clock-util.h"