update priority calculation with source/sink supporting
  + stream is marked as entry stream if a source write on it
  + stream is marked as exit stream if a sink read from it
  + when calculating priority for an entry task, its input (entry)
  stream will not be counted. Similar for exit task, its output (exit)
  stream will not be counted.
support source/sink task & fix some bugs in lpel tests
  + support source/sink task, calculating priority does not count
  entry/exit stream
  + streams written by wrappers are entry streams, and read from
  wrappers are exit streams
  + entry streams are bounded to avoid
  + fix lpel tests: start lpel before creating task
Merge branch 'top_merge' into main_branch