Lots of clean-ups, remove CevallosEngine

* remove CevallosEngine as it is not ready for production use. The
  information-checking part is still available within
  the informationchecking package. The only "supported' CryptoEngine
  is the RabinBenOrEngine for now
* remove unused AbstractICEngine
* remove ImpossibleException in favour of RuntimeExceptions. Some
  occurences have been exchanged with better named exceptions. This
  was done to keep method signatures clean
* move Testhelper from crypto package to archistar-package as other
  subpackages are also using it
* remove unused Shamir-Testcase (was a profiling test case)
* remove SecretSharing-Algorithm Constructors that are supplying
  "Default"-Instances of DecoderFactories (etc.). End-Users should
  always use CryptoEngines and developers should better know which
  sub-components they'd be using
* remove CryptoExcecption -- it was only a wrapper for the generic
  java SecurityException