ENH: add plugin functionnality

Code/Core/otbWrapperApplicationFactory.cxx

Code/Core/otbWrapperApplicationFactory.h

Code/Wrappers/ApplicationLauncherQt/CMakeLists.txt

...appers/ApplicationLauncherQt/otbApplicationLauncherQt.cxx

Code/Wrappers/CMakeLists.txt

Example/Addition/otbAddition.cxx

Example/Addition/otbAddition.h

Example/Smoothing/otbSmoothing.cxx

Example/Smoothing/otbSmoothing.h

Testing/Core/CMakeLists.txt

Testing/Core/otbWrapperApplicationFactoryTest.cxx

Testing/Core/otbWrapperCoreTests.cxx