Ported test_config.cpp from upstream Slic3r.

Extended ConfigBase with set() functions similar to the upstream Slic3r.
ConfigBase::set_deserialize() newly throws if the operation fails.
Extrusion width parameters are newly tested for negative values.

tests/libslic3r/CMakeLists.txt

@@ -2,6 +2,7 @@ get_filename_component(_TEST_NAME ${CMAKE_CURRENT_LIST_DIR} NAME)
 add_executable(${_TEST_NAME}_tests 
 	${_TEST_NAME}_tests.cpp
 	test_3mf.cpp
+	test_config.cpp
 	test_geometry.cpp
 	test_polygon.cpp
 	)