CMake: massive rework for Mac build and other improvements

- macOS: RPATH-related code all removed or disabled
- macOS: new osx/CMakeLists.txt to run some install-code running after all subdirectories
- Assets copying into the runtime output directory implemented for Mac and Linux development

test/CMakeLists.txt

@@ -2,8 +2,8 @@ enable_testing()
 
 set(googleTest_Dir ${CMAKE_CURRENT_SOURCE_DIR}/googletest)
 if(EXISTS ${googleTest_Dir})
-    SET(GTestSrc ${googleTest_Dir}/googletest)
-    SET(GMockSrc ${googleTest_Dir}/googlemock)
+	set(GTestSrc ${googleTest_Dir}/googletest)
+	set(GMockSrc ${googleTest_Dir}/googlemock)
 else()
 	message(FATAL_ERROR "No googletest src dir found!")
 endif()