Added option for additional ranking analysis.  

This adds option to add additional trackers to ranking analysis where ranks are computed normaly and additional trackers are then assigned ranks corresponding to their accuracy and robustness performance compared to normal trackers.

When dealing with tracker identifier understrike ("_") will create subscript for following characker in graph legend, which may look silly for e.g. xxxx_2013. I suggest using "-".  

Also in estimate_accuracy.m and estimate_failures.m there seems to be different format for results from year 2013. Instead of having [2] for failure, they have [NaN, NaN, NaN, -2].
There is no need to change this file, this is just an example. Please write your own analysis scripts in separate files that can be added to the repository after discussion (e.g. I have a lot of analysis scripts that use the toolkit functionality, but I store them locally, because they are useful only to me).