anti spaghetti

I chopped lots of spaghetti out with this rewrite. Here are a few areas:

• module pattern (to be simplified further)
• No global: Iframework used Iframework.shownGraph too much. Now I'm traversing up to the current graph when I need it, which will make subgraphs easier.
• passing graph to node/edge initializer so it is available (this means I have to use a custom .toJSON() to avoid cyclical references when calling JSON.stringify())
• Events: Triggering and listening to events.
• .id prevents duplicate nodes and edges.