This PR adds:
* Renames 'PlatformEK' to 'EK'
* More consistant support of EKs without certificates
* Removes HTTP GET to Intel EK certificate service
* Always populates EK.Public
* Refactor serialized keys into own structure, in preparation for making Key an interface.
* Refactor key logic into separate structures for each platform/TPMversion invariant.
* Implement review feedback