Add back-key exception during fullscreen by default video tag

Add back-key exception during fullscreen by default video tag

[Issue#]     LINUXWRT-1035
[Problem]    In case of fullscreen is enabled by default video tag, back-key works to exit fullscreen.
             However, "tizenhwkey" event also dispatch to application.
[Cause]      Missed to consider.
[Solution]   Move current implementation from wrt-client to view_logic for early return before dispatch "tizenhwkey" event.
[Verification] Install test application attached LINUXWRT-1035.
               Launch application -> change video to fullscreen.
               Select back-key -> Application not terminate
[SCMRequest] N/A

Conflicts:
	src/view/webkit/view_logic.cpp
	src/wrt-client/wrt-client.cpp

Change-Id: I4c8f510281216d95ca170db047f07aeb61b022ab