New Feature: PolicyChangeCount

[LswaN58]

This feature should use the new PerPolicyFeature base class as its base. Like the other Policy features we're adding in this round, it just counts the number of times a new policy card gets selected.

However, in the JSON, we'll want to use a different 'prefix', something like 'plcy' or similar. We'll also need to use a count of 4, since there are 4 different policies.