small fixes (as well as performance fixes)

* remove ByteUtils and do the int->byte conversion manually at
  all 4 lines were it actually was needed
* rename SHA1PRNG into JavaSecureRandom as this explains it's usage
  better
* add a simple NTTShamirTest used for performance analysis
* remove some old debug output
* split out the outgoing-encoding part from the EncodingConverter,
  reduce reallocs. A lot. This should improve performance with
  small fragment sizes