Encrypt metadata (index) too / work on bft f+1 / ss k confusion

Now metadata will be stored using CryptoEngine -- i.e. be encrypted.

ClientResult waited for f+1 results -- this is too low if we want to
do Shamir Secret Sharing. Actually this is rather ugly right now,
I really need to switch to robust secret sharing to make this work.

In addition the behavior should configure itself automagically --
somehow ClientResult should now the expected behavior is defined
by the used CryptoEngine. How to integrate this in a clean manner?