Motion graph

This is a branch with a simple motion graph implementation. It also required to include a number of novel features for the animation class (e.g., building a proxy). The computation of the metrics has also been optimized, so that animations/frames are "prepared" in advance (i.e., what elements will be required for computing the similarity between frames) and this "prepared" data is then used to compute the similarity. This avoids computing elements for the same frame a number of times.