Build System out of date

[sleistikow]

Unfortunately, Voreen's build system and libraries have become outdated.

This is a short summary of major points required to update the build system and libraries.

• Make Voreen Modules own CMake targets. This immensly speeds up builds if a module was added/removed.
• Use (at least!) c++17. C++20 would be desirable.
• Switch to Qt6 (requires c++17).
• Remove boost in favor of the STL, All used boost features should now be part of the STL.
• Remove or update outdated modules (s.a. ffmpeg. itk)
• Use modern CMake: - meanwhile, some dependencies such as VTK removed support for manually adding libraries and headers.
• Use some package manager such as vcpkg or CPM.