(core): use lambdas instead of deprecated QSignalMapper for Qt Signals/Slots

Summary

QSignalMapper is clearly marked as deprecated in Qt Doc:

This class is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

• sight/modules/ui/uiImageQt/include/uiImageQt/WindowLevel.hpp
• sight/modules/ui/uiImageQt/src/uiImageQt/WindowLevel.cpp
• sight/modules/ui/monitorQt/include/monitorQt/DumpEditor.hpp
• sight/modules/ui/monitorQt/src/monitorQt/DumpEditor.cpp
• sight/modules/ui/guiQt/include/guiQt/editor/SParameters.hpp
• sight/modules/io/ioDicom/src/ioDicom/SFilterSelectionEditor.cpp

Possible fixes

Replace the QSignalMapper by a simple lambda as in:

connect(watchThisButton, &QPushButton::clicked, this, [this](){ slotLinkActivated(QStringLiteral("add_watch")); });