Experimental-ish rollback functionality

builtin/chatcommands.lua

builtin/privileges.lua

doc/lua_api.txt

src/CMakeLists.txt

src/content_abm.cpp

src/content_cao.cpp

src/content_cso.cpp

src/environment.cpp

src/environment.h

src/gamedef.h

src/inventorymanager.cpp

src/map.cpp

src/map.h

src/rollback.cpp

src/rollback.h

src/rollback_interface.cpp

src/rollback_interface.h

src/scriptapi.cpp

src/server.cpp

src/server.h