Merge DSIGN and KES classes

[tdammers]

This changes things as follows:

DSIGN:

• The DSIGNMAlgorithmBase class disappears; its functionality is provided by the existing DSIGNAlgorithm class
• The DSIGNMAlgorithm class remains, but becomes a subclass of DSIGNAlgorithm
• Any methods and types from DSIGNMAlgorithmBase that do not involve sign keys or seeds will be shared between the pure (DSIGNAlgorithm) and mlocked (DSIGNMAlgorithm) APIs, since we only need to mlock seeds and sign keys. The M flavors of those methods and types have been deleted.
• The same phantom types are used for the pure and mlocked (if supported) flavors of DSIGN algorithms
• The distinction between pure and mlocked APIs is made by using the pure or mlocked sign key and seed types, and the pure or mlocked flavors of the corresponding methods (genKeyDSIGN(M), deriveVerKeyDSIGN(M), etc.). All DSIGN algorithms must support a pure API (DSIGNAlgorithm); those that also support mlocked DSIGN (currently only ED25519) additionally support DSIGNMAlgorithm.
• As a consequence, the signatures and verification keys produced and used by the pure and mlocked flavors of the same DSIGN algorithm are exactly the same.

KES:

• KESSignAlgorithm has been merged into KESAlgorithm, which now offers the full range of KES operations. Since the mlocking monad (m) is no longer a typeclass parameter, the split is no longer necessary, and conceptually, it does not make sense to have a KES algorithm that can only verify, but not sign.

[tdammers]

Depends on #404.

[lehins]

Love it!