Grouping/ungrouping algorithm seems finished, done minor refactor. Finished...

Grouping/ungrouping algorithm seems finished, done minor refactor. Finished test "complex 1". Fix GraphNode: transition on removed node allowed user to interact with it, triggering error when getting node from store/data. #13

Grouping would like a refactor.
Also, the randomized test over big dataset is failing so there may be a corner case yet to be discovered. Not sure if bug, it may be also triggered by a bug in dataset.