WIP node metadata, node timers

src/CMakeLists.txt

src/content_nodemeta.cpp

src/content_nodemeta.h

src/environment.cpp

src/game.cpp

src/map.cpp

src/map.h

src/mapblock.cpp

src/mapblock.h

src/nodedef.cpp

src/nodedef.h

src/nodemetadata.cpp

src/nodemetadata.h

src/nodetimer.cpp

src/nodetimer.h

src/scriptapi.cpp

src/serialization.h

src/server.cpp

src/server.h