resource-container: add method to manually send a notification

resource-container: add method to manually send a notification

When I am setting more than one attribute at a time I only want to send one
notification after all the attributes have been set. This change makes it
possible to send the notification at the end.

Change-Id: I8a4825edab97b92041a67a8cdf57f9a6fd832f3b
Signed-off-by: Hauke Mehrtens <hauke.mehrtens@lantiq.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/4207
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Markus Jung <markus.jung85@gmail.com>
Reviewed-by: Madan Lanka <lanka.madan@samsung.com>