Allow all policies to inherit defaults

Previously, all declared policies had to implement every tag required by the policy, even if it was the same as the default. In addition to being annoying, this makes us less forward compatible because if we add a new item to the policy any unchanged policy would become incorrect.

This change moves the default policy declarations from the default policy to PolicyBase. The default policy inherits all of them without any change. Other policies need only override those that are different than the default.