fix(the-graph-app): fix offset of edge

fix offset of edge when the graph is not at top: 0, left:0
fix(the-graph-app): move offset modification

move offset modification to source of position to account for scale
feat(event-listeners): add event listeners

add event listeners for graph changed, state/pan changed and moved node
Merge pull request #1 from fabiancook/feature/event-listeners

Feature/event listeners