release charts

charts for each iteration are useful, but it would also be nice to see charts for the whole release to evaluate its health and progress.

completed graph can be built by simply combining iteration completed graphs (would be cool to color background section corresponding to each iteration to mark it on the whole graph)

estimaton graph might not be so simple since new items might be added between iterations. it probably doesn't matter though. it's possible to just connect estimation of one iteration with estimation in the other. in most cases iterations would be very close to each other.