added the clear button

src/gui/official/JPushButton.cpp

src/gui/official/PhoneLine.cpp

src/gui/official/PhoneLine.hpp

src/gui/official/PhoneLineManagerImpl.cpp

src/gui/official/PhoneLineManagerImpl.hpp

src/gui/official/SFLPhoneApp.cpp

src/gui/official/SFLPhoneWindow.cpp

src/gui/official/SFLPhoneWindow.hpp

src/gui/official/sflphone.qrc