Add Priority Mail Regional and Flat Rate Pricing to Rate Calculator

[TrollHoardGames]

Add Priority Mail Regional and Flat Rate pricing to Rate Calculator. Sometimes the cubic / general PM rates are significantly different from the Regional Rate pricing, and it would be useful to see this in one place rather than memorize zone pricing or have to change the package type each time.

[Kilo78]

Yes, this would help a lot as our label makers don't always think, hey! this would be cheaper if we used cubic pricing when looking at the calculator.