New Hash transformer implementation and validation warning fixes

[wwoytenko]

New Hash transformer implementation and validation warning fixes

• New Hash transformer uses sha1 hash by default.
• Added parameter function that can provide a choice of possible hash algorithms md5, sha1, sha256, sha512.
• Added max_length parameter allowing to truncate hash tail higher than provided length. The default value is 0 - meaning "do not truncate"
• Fixed metadata enrichment for validation warnings caused by RawValueValidator

Example:

- schema: "humanresources"
  name: "employee"
  transformers:
    - name: "Hash"
      params:
        column: "loginid"
        function: "sha1"
        max_length: 10

Additional changes:

• Added Error severity for Cmd parameter validator

Closes #8