Added more training cases: Cross-task now has a 0% training and a 20% training variant
			   Cross-agent now has a 0% training and a 20% training variant

Added smarter method for dealing with limited data in the TP and MP computation -- instead of plugging in an ideal value, it now leaves it out of the computation entirely, and returns a default value (0.) if there isn't enough information to determine a proper answer.
Added a floor of 0 ms to estimate_skill_duration.