Merge branch 'cleanup-legacy-workaround' into mh-ci

CMakeLists.txt

 include (plugin)
 
-if(APPLE)
-    # actually we currently need this for any libc++ platform
-    # compare issue 136:
-    # https://www.graphics.rwth-aachen.de:9000/OpenFlipper-Free/OpenFlipper-Free/issues/136
-    add_definitions(-DOVM_FORCE_STATIC_CAST)
-endif()
-
 openflipper_plugin (INSTALLDATA Icons Shaders
                     DIRS OpenMesh OpenVolumeMesh Widgets ScriptObjects Toolbars Models Nodes PropertyVisualizer
                     DEPS OpenMesh