Speedup changes for real-time graphs

I have done some modifications to the original code:
1) to increase the performance of real-time graphs as well as very large data sets.
My changes uses a different data structures and therefore will not be 100% compatible with the existing code and might therefore will require some changes to work with this. I can make a different constructor that will ensure compatibility if you are interested in merging it with your code.
2) changed the scroll, fling and zoom interaction.