Generate PG from SFG

Description of issue:

Given a valid SFG, then a PG (presedence graph) should be able to be generated. The PG should describe the order of how operations are done given input and output in a SFG.

Linked Requirements:

( 37, 38 )

Potential Issues:

None

Blockers:

( #12 (closed) )

Issue Requirements:

1. Given a valid SFG, then a new PG should be able to be created.
2. The resulting PG should be correct according to the description of a PG.

Comment:

Please see the course page for more information on what a PG is and what it should represent.

User stories:

1. As a user I want to be able to generate a precedence graph from an SFG.
2. As a developer I want to be able to extract the cyclic precedence of the operations in an SFG from the precedence graph.