Mixin Events to Graph.prototype in proto factory.
That way subclasses of Graph won't need to do that themselves.
Graph.merge: fix scoping issue
rename: __prototype__ => Prototype
I.e., a compound is treated as it was applied flattened. This has the effect that all listeners are called after each sub-operation which makes things much easier with co-transformations.
I.e., instead of updating indexes via 'operation:applied' events, they are updated by the graph explicitely.
After fixing a bug in Graph an error in the Graph Event Test has been revealed.
Added dedicated test.
Now there is global 'operation:applied' which is called on each applied (atomic) operation. Dedicated events are fired for: node:created, node:deleted, property:set, property:updated