"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"
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.
