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/cryptsetup/cryptsetup.c

@@ -19,11 +19,11 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
-#include <string.h>
 #include <errno.h>
-#include <sys/mman.h>
-#include <mntent.h>
 #include <libcryptsetup.h>
+#include <mntent.h>
+#include <string.h>
+#include <sys/mman.h>
 
 #include "sd-device.h"
 
@@ -33,6 +33,7 @@
 #include "fileio.h"
 #include "log.h"
 #include "path-util.h"
+#include "string-util.h"
 #include "strv.h"
 #include "util.h"