core: split "nm-core-utils.h" out of "NetworkManagerUtils.h"

"NetworkManagerUtils.h" contains a bunch of helper tools for core
daemon ("src/").

Unfortunately, it has dependencies to other parts of core,
such as "nm-device.h" and "nm-platform.h". Split out a part
of tools that are independent so that they can be used without
dragging in other dependencies.

"nm-core-utils.h" should only use libnm-core, "nm-logging.h"
and shared.

"NetworkManagerUtils.h" should provide all "nm-core-utils.h" and
possibly other utilities that have larger dependencies.

src/platform/nm-platform-utils.c

@@ -18,6 +18,8 @@
  * Copyright (C) 2015 Red Hat, Inc.
  */
 
+#include "nm-default.h"
+
 #include "nm-platform-utils.h"
 
 #include <string.h>
@@ -30,10 +32,9 @@
 #include <linux/version.h>
 
 #include "nm-utils.h"
-#include "NetworkManagerUtils.h"
-#include "nm-default.h"
 #include "nm-setting-wired.h"
 
+#include "nm-core-utils.h"
 
 /******************************************************************
  * ethtool