Change include management.

Now subdirectory must be specified. The main reason for this change, is that this explicitely sets where the file is. Moreover, it "simplifies" CMakeLists.txt files.

added 1 commit

• 36cc38a9 - Fix missing includes for g++-8 and clang++-8

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enabled an automatic merge when the pipeline for 36cc38a9 succeeds

merged

mentioned in commit b66f11b0