Separate sign and verify from cipher and create new interface

Since we have implemented ECDSA, it became more obvious that current <cipher> does not fit to the cryptographic model we are providing. More precisely, DSA and ECDSA doesn't support any encryption and decryption yet still populate something (like not implemented or unsupported operation error procedures).

So it's nice to separate these and only provides required field.

NOTE: we must provide backward compatible way.