ENH: add GetParameterByKey to ParameterGroup

Code/Core/otbWrapperApplication.cxx

Code/Core/otbWrapperApplication.h

Code/Core/otbWrapperChoiceParameter.h

Code/Core/otbWrapperParameterGroup.h

Code/Wrappers/QtWidget/otbWrapperQtWidgetModel.cxx

Code/Wrappers/QtWidget/otbWrapperQtWidgetParameterGroup.cxx

Code/Wrappers/SWIG/otbApplication.i

Example/Addition/otbAddition.cxx

Example/Smoothing/otbSmoothing.cxx