Resolve "Debug under MSVC linker Error"

From the issue:

This is because of the following part of the CMakeLists.txt

# Debug Version of slows our debug down to a unusable degree
set_target_properties(${OpenCV_LIBS} PROPERTIES
    MAP_IMPORTED_CONFIG_DEBUG RELEASE
    MAP_IMPORTED_CONFIG_RELWITHDEBINFO RELEASE)

This tries to link against release OpenCV even in debug, which doesn't work since the MSVC CRT ABI changes between release and debug.

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We do now only do the remapping from debug to release when not using MSVC. This leads to the debug build of MSVC being significantly slower than the corresponding build in GCC or clang, but at least it's possible and non-performance ciritical debugging might be easier, now that one can compile without optimizations.

Closes #225 (closed)

Reviewer Checklist

Formatting

• the pre-build checks succeed

General code quality

• naming conventions are met (see .clang-tidy for detailed information)
• no static analyzer warnings in new code parts (e.g., use clang-tidy for checking)

General usability

• old versions of pet-files are still loadable

Only if changes in UI

• new elements are also saved and loaded from pet-file
• check if tab order is still correct
• all new SpinBoxes are promoted
• new keybindings added to Petrack::keyBindings()