#10 Bug in GraphNodeAddIncomingEdgeWithTags

[Jeremy Lewi]

GraphNode.addIncomingEdgeWithTags doesn't actually store the tags.
Also, I think we need to modify the schema for EdgeData so that we associate a direction with each read_tag.
For example,
suppose we have the read "CGTC" which gives rise to the edge
CGT->GTC
Now when we add the incoming edge to GTC , we flip the edge because we only store the outgoing edges in a node. So when we store the read tag with this thread, we need to add a flag which tells us whether it goes with the outgoing edge or the incoming edge corresponding to the complement strand of the edge stored in the node.

We should increase test coverage to cover this.