Choose timebag evolution model and work a little on presentation

We want to scale down all but the first row of histograms to have the
first row pop out. That's done. Also, we need to add a time line below
the first row, and x titles.
Cosmetic changes for timebag evolution figure

* Added an arrow for time
* Downscaled all but the first row
* Added 'bag X' titles for x axes for the first row
Better centering for feature variation figures