Add missing license files.

The files:
 src/ExportManager.cpp
 src/ExportManager.h
 src/Gui/ExportMenu.cpp
 src/Gui/ExportMenu.h
 src/Gui/KSImageWidget.cpp
 src/Gui/KSImageWidget.h
 src/Gui/KSMainWindow.cpp
 src/Gui/KSMainWindow.h
 src/Gui/KSSaveConfigDialog.cpp
 src/Gui/KSSaveConfigDialog.h
 src/Gui/KSWidget.cpp
 src/Gui/KSWidget.h
 src/Gui/SmartSpinBox.cpp
 src/Gui/SmartSpinBox.h
 src/KipiInterface/KSGKipiImageCollectionShared.cpp
 src/KipiInterface/KSGKipiImageCollectionShared.h
 src/KipiInterface/KSGKipiInfoShared.cpp
 src/KipiInterface/KSGKipiInfoShared.h
 src/KipiInterface/KSGKipiInterface.cpp
 src/KipiInterface/KSGKipiInterface.h
 src/PlatformBackends/DummyImageGrabber.cpp
 src/PlatformBackends/DummyImageGrabber.h
 src/PlatformBackends/ImageGrabber.cpp
 src/PlatformBackends/ImageGrabber.h
 src/PlatformBackends/X11ImageGrabber.cpp
 src/PlatformBackends/X11ImageGrabber.h
 src/SpectacleCore.cpp
 src/SpectacleCore.h
 src/SpectacleDBusAdapter.cpp
 src/SpectacleDBusAdapter.h
Are licensed under the LGPL-2+ and the files:
 src/Gui/ScreenClipper.cpp
 src/Gui/ScreenClipper.h
Are licensed under a LGPL-2 only. Since the LGPL requires a copy of the
license to be distributed with these files I'm adding these files.