Remove CryptoExt class in favor of friendship

Remove CryptoExt class in favor of friendship

In the ckm_db_tool CLI helper project, CKMLogicExt and CryptoExt classes
are responsible for breaking encapsulation of CKMLogic and Crypto
classes. However, code used for extracting a Crypto member and casting
it to the CryptoExt type is repeated two times (soon three), and rather
dangerous.

This refactor makes CKMLogicExt a friend of the Crypto class. This makes
it possible to implement additional methods directly in CKMLogicExt
without doing dangerous slicing object casts.

Change-Id: Ice7261b76f46f9a6206f7ae1faded1f3d8e359cb