The fact that NMRemoteConnection has to be an NMConnection and
therefore can't be an NMObject means that it needs to reimplement bits
of NMObject functionality (and likewise NMObject needs some special
magic to deal with it). Likewise, we will need a daemon-side
equivalent of NMObject as part of the gdbus port, and we would want
NMSettingsConnection to be able to inherit from this as well.

Solve this problem by making NMConnection into an interface, and
having NMRemoteConnection and NMSettingsConnection implement it. (We
use some hacks to keep the GHashTable of NMSettings objects inside
nm-connection.c rather than having to be implemented by the
implementations.)

Since NMConnection is no longer an instantiable type, this adds
NMSimpleConnection to replace the various non-D-Bus-based uses of
NMConnection throughout the code. nm_connection_new() becomes
nm_simple_connection_new(), nm_connection_new_from_hash() becomes
nm_simple_connection_new_from_hash(), and nm_connection_duplicate()
becomes nm_simple_connection_new_clone().

NMRemoteSettings duplicates a bunch of NMObject's functionality that
it doesn't need to. In libnm-glib, it wouldn't have been possible to
port NMRemoteSettings to NMObject without breaking ABI, but now in
libnm we can do that.

As a side effect of this, NMRemoteSettings gains a "connections"
property, and "connection-added" and "connection-removed" signals
(with the former replacing the old "new-connection" signal). This also
removes the "connections-loaded" signal, since the connections will
now always be loaded (via the initialization of the "connections"
property) during init()/init_async().

Also, this removes NMRemoteConnection's "removed" signal, since it's
redundant with the new NMRemoteSettings::connection-removed (and
having the signal on NMRemoteSettings instead is more consistent with
other objects).

Rename NMClient:manager-running and NMRemoteSettings:service-running
to both be :nm-running.

Add NetworkManager.h, which includes all of the other NM header, and
require all external users of libnm to use that rather than the
individual headers.

(An exception is made for nm-dbus-interface.h,
nm-vpn-dbus-interface.h, and nm-version.h, which can be included
separately.)

"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"

Remove _nm_object_ensure_inited(), etc; objects that implement
GInitable are now mandatory-to-init().

Remove constructor() implementations that sometimes return NULL; do
all the relevant checking in init() instead.

Make nm_client_new() and nm_remote_settings_new() take a GCancellable
and a GError**.

Most D-Bus interface name macros used "INTERFACE" in their name (eg,
NM_DBUS_INTERFACE), but a few used "IFACE" instead (eg,
NM_DBUS_IFACE_SETTINGS). Make them consistent.

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.

nm-version.h was getting disted, making srcdir!=builddir work for
tarball builds, but not for git builds.

Also, remove "-I${top_builddir}/include" from all Makefile.ams, since
there's nothing generated in include/ any more.

NetworkManager.h, NetworkManagerVPN.h, and nm-version.h are part of
the libnm-util API, so move them to libnm-util.

include/ still contains headers that are strictly NM-internal (eg,
nm-glib-compat.h).