Add "Explanation" section to show calculation involved in breeding time estimates

[tylercamp]

Breeding time estimates are useful but it's not immediately obvious how Pal Calc makes the estimate. Some docs are available [1] [2] but they are complex and hard to check against the basic output from Pal Calc.

It would be useful (for various reasons) for Pal Calc to also show the list of calculations and probabilities involved in the final time estimate.