New mime types in SessionXML and minor renaming

GUI/coregui/Models/FitParameterAbsModel.cpp

GUI/coregui/Models/FitParameterAbsModel.h

GUI/coregui/Models/ParameterTuningModel.cpp

GUI/coregui/Models/SessionModel.cpp

GUI/coregui/Models/SessionXML.h

GUI/coregui/Views/FitWidgets/FitParameterWidget.cpp

GUI/coregui/Views/FitWidgets/FitParameterWidget.h

GUI/coregui/Views/FitWidgets/FitSuiteWidget.cpp

GUI/coregui/Views/FitWidgets/FitSuiteWidget.h

GUI/coregui/Views/FitWidgets/TestFitWidgets.cpp

GUI/coregui/Views/FitWidgets/TestFitWidgets.h

GUI/coregui/Views/SampleDesigner/ItemTreeView.cpp