Fix for IOT-927 resource container attribute update/notify race condition

Fix for IOT-927 resource container attribute update/notify race condition

- Asynchronous notification of observing clients
- Mutex for access on RCSResourceAttributes
- returning RCSResourceAttributes by value
- reference to const RCSResourceAttributes for handleSetAttributeRequest API

Note: The change breaks backward compatibility with previous APIs

Change-Id: I2f84353aa993772e7a1a908c766c77786fe7c3ea
Signed-off-by: Markus Jung <markus.jung@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/4913
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Madan Lanka <lanka.madan@samsung.com>
Reviewed-by: George Nash <george.nash@intel.com>
Reviewed-by: JungHo Kim <jhyo.kim@samsung.com>
Reviewed-by: Uze Choi <uzchoi@samsung.com>