[ #63393 ] Update copyright for 2015

src/abstractbookmarkmodel.cpp

src/abstractbookmarkmodel.h

src/abstractitembackend.cpp

src/abstractitembackend.h

src/abstractitembackendmodelextension.cpp

src/abstractitembackendmodelextension.h

src/account.cpp

src/account.h

src/accountmodel.cpp

src/accountmodel.h

src/audio/alsapluginmodel.cpp

src/audio/alsapluginmodel.h

src/audio/codecmodel.cpp

src/audio/codecmodel.h

src/audio/inputdevicemodel.cpp

src/audio/inputdevicemodel.h

src/audio/managermodel.cpp

src/audio/managermodel.h

src/audio/outputdevicemodel.cpp

src/audio/outputdevicemodel.h