Port the dbus-glib-based examples to GDBus.
Also, don't use libnm in them at all; there's not much point in
examples that use the D-Bus API directly if they're just going to fall
back to libnm for the hard stuff... (And also, this avoids the problem
that GDBus uses GVariant, while the libnm-core APIs currently still
use GHashTables.)
Also fix up some comment grammar and copyright style, and add emacs
modelines where missing.
Also rename the existing GDBus-based examples to have names ending in
"-gdbus", not "-GDBus", since there's no reason to gratuitously
capitalize here.
"NetworkManager.h"'s name (and non-standard capitalization) suggest
that it's some sort of high-level super-important header, but it's
really just low-level D-Bus stuff. Rename it to "nm-dbus-interface.h"
and likewise "NetworkManagerVPN.h" to "nm-vpn-dbus-interface.h"
Since the API has not changed at this point, this is mostly just a
matter of updating Makefiles, and changing references to the library
name in comments.
NetworkManager cannot link to libnm due to the duplicated type/symbol
names. So it links to libnm-core.la directly, which means that
NetworkManager gets a separate copy of that code from libnm.so.
Everything else links to libnm.
