Digest changes plus some

[conniey]

Fixes:

• DataTypeConverter is removed in JDK 11. Removes this reliance in DIgestChallengeProcessor to future-proof it.
• Instantiates MessageDigest and SecureRandom because creating the message digest is a long process and creating the SecureRandom each time getHeader is called could result in the same seed.
• There was a warning about it being platform dependent because using CP1252 encoding. Changed to use UTF-8 source encoding
  • Reference
• Fixes checkstyle issues
  • Rules export import statements to be alphabetically ordered with static imports first.
  • Expands * imports
• Cleaning up DigestChallengeProcessor with a getHexValue method.

[conniey]

Closing for now because it is not a mandatory change.