Support Source/Sink tasks
   + an entity is mapped to a source/sink task if it is specified with a positive location, e.g. box@1 (this will be modified later to support more types of manual mapping)
   + a source/sink task is executed separately on its own thread (for more detail, see LPEL_FLAG)
- Update LOGFORMAT for centralQ approach
- Add LPEL_FLAGS for more detail of flag usage in LPEL