Add properties to track the "primary" connection (ie, the active
connection with either the default route, or the route to the VPN with
the default route), and the active connection that is currently
activating, and likely to become the :primary-connection when it
completes.
https://bugzilla.gnome.org/show_bug.cgi?id=704841
NMSysconfigSettings has the authoritative list of connections, no reason
to duplicate all that tracking code in NMManager. Add the missing bits
that the manager had to NMSysconfigSettings, and point NMPolicy at the
settings object instead of NMManager for that.
