Initial merge in of the DataExplorer.

Gui/Base/CMakeLists.txt

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

Gui/Base/StrictDoubleValidator.h

Gui/Base/StrictIntValidator.h

Gui/Base/TreeItem.cpp

Gui/Base/TreeItem.h

Gui/Base/TreeModel.cpp

Gui/Base/TreeModel.h

Gui/Base/TreeModelIterator.cpp