Modified SFG after rescheduling

The Schedule class contains two SFGs:

1. self._original_sfg which is a copy of the original SFG
2. self._sfg which is a version without delays for scheduling

Accessing the sfg property returns self._original_sfg. It would make sense to return a recreated copy of self._sfg where the delays are reintroduced based on rescheduling (so it may be retimed and/or pipelined). Also, this would reduce the need to store a copy of the original SFG.