Split ObjDef/ObjDefManager out to objdef.cpp

build/android/jni/Android.mk

src/CMakeLists.txt

src/mapgen.cpp

src/mapgen.h

src/mg_biome.h

src/mg_decoration.h

src/mg_ore.h

src/objdef.cpp

src/objdef.h

src/unittest/test_objdef.cpp

src/util/string.h