Added license text to everything in Gui-subfolder.

FemLib/BoundaryCondition.cpp

FemLib/BoundaryCondition.h

FemLib/InitialCondition.cpp

FemLib/InitialCondition.h

FemLib/SourceTerm.cpp

FemLib/SourceTerm.h

FileIO/GMSInterface.cpp

FileIO/GMSInterface.h

Gui/Base/CheckboxDelegate.cpp

Gui/Base/CheckboxDelegate.h

Gui/Base/ColorPickerPushButton.cpp

Gui/Base/ColorPickerPushButton.h

Gui/Base/OGSError.cpp

Gui/Base/OGSError.h

Gui/Base/QNonScalableGraphicsTextItem.cpp

Gui/Base/QNonScalableGraphicsTextItem.h

Gui/Base/QValueTooltipSlider.cpp

Gui/Base/QValueTooltipSlider.h

Gui/Base/RecentFiles.cpp

Gui/Base/RecentFiles.h