Added edge statements with subgraphs as nodes to DOT file. Basically, if source node is a subgraph, all its vertices are connected to all the vertices of the target node, and vice verse.

Added supergraph, queryCallback, and warningCallback as arguments for EdgeStatement in order to have subgraph statements as nodes in EdgeStatements.4

Changed DOTGraphs to store supergraph nodes and edges separately to allow for subgraphs as nodes.
Fixed tgf file not exporting edges.
Fixed typo in tgf file
Merge branch 'master' of https://github.com/ulethHCI/GLuskap