Implements some function for check busname is existed

Implements some function for check busname is existed

 - Before sending an event to the notification caller using the
   notification_send_event() API, check if the busname exists.
 - By using hashtable data-structure, the priv_id of notification_h
   and the busname are managed.
 - Check by watching the busname of the app that posted the
   notification.

related with
patch : https://review.tizen.org/gerrit/#/c/108771/
API : notification_check_event_sender()

Signed-off-by: seungha.son <seungha.son@samsung.com>
Change-Id: Ie92a1c5e7ac46cc4d2aa2902f35043861f65c814