Simplified DataLine and SpaceConverterNode usage
Fixed DataLine bug from previous commit
Fixed DataNode serialization setup

Now uses macros MAKE_NODE_READABLE_H and MAKE_NODE_READABLE_CPP in each
child DataNode to initialize it at program startup to be readable.
Updated serialization/shader generator stuff
Fixed xml serialization bug
Updated rendering systems for newest DataNode interface
Updated worlds to use new DataNode system
Added test in main.cpp for material serialization