shared: move most of "shared/nm-utils" to "shared/nm-glib-aux"

From the files under "shared/nm-utils" we build an internal library
that provides glib-based helper utilities.

Move the files of that basic library to a new subdirectory
"shared/nm-glib-aux" and rename the helper library "libnm-core-base.la"
to "libnm-glib-aux.la".

Reasons:

 - the name "utils" is overused in our code-base. Everything's an
   "utils". Give this thing a more distinct name.

 - there were additional files under "shared/nm-utils", which are not
   part of this internal library "libnm-utils-base.la". All the files
   that are part of this library should be together in the same
   directory, but files that are not, should not be there.

 - the new name should better convey what this library is and what is isn't:
   it's a set of utilities and helper functions that extend glib with
   funcitonality that we commonly need.

There are still some files left under "shared/nm-utils". They have less
a unifying propose to be in their own directory, so I leave them there
for now. But at least they are separate from "shared/nm-glib-aux",
which has a very clear purpose.

(cherry picked from commit 80db06f768)

src/nm-netns.c

@@ -22,7 +22,7 @@
 
 #include "nm-netns.h"
 
-#include "nm-utils/nm-dedup-multi.h"
+#include "nm-glib-aux/nm-dedup-multi.h"
 
 #include "NetworkManagerUtils.h"
 #include "nm-core-internal.h"