Don't forget to activate a connection if we show a dialog when activating

addAndActivate in some cases will show the connection editor dialog. In
that case, once the dialog is confirmed, we would call "addConnection"
rather than "addAndActivateConnection", so one would need to manually
connect to the now correctly configured network again. Instead, move the
"addAndActivate" dbus call to its own method so we can call it in the
signal handler rather than calling only addConnection.