• Create AbstractCryptClass for Unix-Crypt-based algorithms (e.g. bcrypt, script, argon2)
• Move some of the password matching logic into the Hash classes
  Reviwers: Review method placement and HAsh class description.
• removed hashrequest
• API change: made salt not-nullable.
  Additional constructor is supplied for hashing without or with
  default salt, the former and other methods/fields using
  SimpleByteSource.empty().
  Reviewers: Pay attention to method logic, so no empty salt is
  being used where a former null value would have created a
  new, random salt.
• Modified tests to not expect exceptions in certain cases.
• Modified tests to not expect passwordService calls when supplying an
  existing hash.
• Fix Javadocs
• Fix Hasher utility
• Add Argon2 algorithms
• Deprecate old non-KDF hash classes
• Also print warnings when encountering the old hashes
• What should getBytes() return? There is no overridden Javadoc. Currently, only the hashed data is returned, but maybe it was meant to also return the hash here? If not, why even implement CodecSupport? This needs to be clarified before merging.
  => This is more important if we want to retain Hex and Base64 formats. They need all parameters encoded.
• BCrypt iterations vs cost: What do we return for getIterations()? Currently I return the cost. But we could also return the real iterations (which is 2^cost) it that made sense.
• How to store argon2 parameters in Shiro1CryptFormat? Maybe create a Shiro2 CryptFormat?
  Argon2 outputs this: $argon2i$v=19$m=65536,t=2,p=4$c29tZXNhbHQ$RdescudvJCsgt3ub+b+dWRWJTmaaJObG.
  The Shiro1 crypt format only has: prefix(shiro1), algo, iterationcount, salt, hash.
  We would also need version and parameters or so, which could be empty for others.
  The current working copy uses a comma separated list for the iterationCount field, but I am not happy with that.
• Shiro2CryptFormat (see comment above)?
• revert Shiro1CryptFormat modifications?
• Can we drop Hex and Base64 Formats? => Can be done in another PR.
• Add more tests for bcrypt and argon2.
• Tune Argon2 default parameters. Target computation time on servers: ~ 0.1s as per RFC recommendation.
• Add scrypt. It is better than bcrypt. => Another PR.
• What does DefaultPasswordService.testStringComparisonWhenNotUsingAParsableHashFormat actually test? It only works if specific parameters are set.

API Changes

• Changed default DefaultPasswordService.java algorithm to "Argon2id".
• PasswordService.encryptPassword(Object plaintext) will now throw
  a NullPointerException on null parameter. It was never specified how this method would behave.
• made salt not-nullable.

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