Implement graph structure for toDot

[Aaron3154518]

I propose a graph implementation of the dot structure for easier manipulation.

Objects:

• CompGraph - Main graph object, contains two maps which pair statement indices : statement nodes and dataspace names : dataspace nodes
• Node - represents a graph node for either a statement or a dataspace. Contains two vectors of Edge pointers, one for out-facing edges and one for in-facing edges.
• Edge - represents an edge node. Contains a statement index and a data space name. Contains a boolean describing its write/read status. Also contains the access relation for its dataspace.

In Computation, we would just create a new CompGraph, call any manipulation functions, and call toDotString()

[Aaron3154518]

Graph structure has been created and results are the same as previous dot files.