we can process hangup events

src/gui/official/Call.hpp

src/gui/official/Event.cpp

src/gui/official/Event.hpp

src/gui/official/PhoneLine.cpp

src/gui/official/PhoneLine.hpp

src/gui/official/PhoneLineManager.cpp

src/gui/official/PhoneLineManagerImpl.cpp

src/gui/official/PhoneLineManagerImpl.hpp

src/gui/official/images/clear_off.png

src/gui/official/images/clear_on.png