break dependency to Ewk_Notification

break dependency to Ewk_Notification

- Added tizen_webview::Notification class which uses existing _Ewk_Notification
  as its implementation.

- Replaced include guard for ewk_notification_private.h to avoid conflict with
  ewk side header. The file name should be renamed in next refactoring.

- Deleted redundant NotificationControllerEfl::RemoveClosedNotifications()
  which can be implemented in ewk side using other method, hence not fundamental.

Issue: CBEFL-92, CBWEBVIEW-386
Change-Id: Iaecce42cfc047915356b7cdf9226e8bba5a16ff7
Signed-off-by: SeungSeop Park <sns.park@samsung.com>
Conflicts:
	impl/API/ewk_notification_private.cc
	impl/content_main_delegate_efl.cc