Ported test_support_material from upstream Slic3r.

Reworked the FFF testing framework & ConfigBase::set_deserialize()
for more compact tests: set_deserialize() now accepts list
of key / value pairs.

Fixed an incorrect assert in LayerRegion.

tests/fff_print/CMakeLists.txt

@@ -11,6 +11,7 @@ add_executable(${_TEST_NAME}_tests
 	test_printgcode.cpp
 	test_printobject.cpp
 	test_skirt_brim.cpp
+	test_support_material.cpp
 	test_trianglemesh.cpp
 	)
 target_link_libraries(${_TEST_NAME}_tests test_common libslic3r)