Occupancy operator model

[jessiejofielding]

Overview

Make changes to the likelihood calculation for the occupancy operator model.

Changelog

Features and main model changes

• add new occupancy likelihood calculation (AncestralStateMinimumSwitchTreeLikelihood.java)
• add a new class to refactor the trait linked clock model that works with the occupancy operator (OccupancyLinkedClockModel.java)
• add new operator that can honor the constraints of the new likelihood method (TraitAndOccupancyTreeOperator.java)
• update version file to include new models

Testing