Thanks to Stefan Karlsson for helping with the implementation.
Also add SASLMechanism.checkIfSuccessfulOrThrow(), to increase the
security by verifying the mechanisms state at the end of SASL
authentication.
SASLMechanism now has a SASLPrep StringTransformer.
Refactor SHA1 functions out of StringUtils into SHA1 utility class.
Add MAC utility class.
Make DummyConnection getSentpacket() methods use generics to make unit
testing SCRAM-SHA1 easier.
Fixes SMACK-398
Florian Schmaus