Implementation of response of group action (for remote resources)

Implementation of response of group action (for remote resources)

There is no response when resource client send message[POST]
to a group with GROUP_INTERFACE, so client cannot receive any message.

We provide logic about the aggregation of children' response.
Then, merged response will be delivered to client.

Additionally, regarding Sudarshan Prasad's comment of previous commit.
We change the definition of GROUP_INTERFACE.

Change-Id: I6c2550472d1e02cd2606317fcb1796e59e004b78
Signed-off-by: HyunJun Kim <hyunjun2.kim@samsung.com>