ENG-4791, ENG-4674 (partial):

Move the UTF8ENCODING constant to new file/package
org.voltdb.common.Constants
Remove inclusion of ZK libraries in the client jar.
Modify voter so that it explicitly uses the voltdb java client library
and the bare minimum of known external jars to run clients.
Merge pull request #577 from VoltDB/eng4791

Eng4791, eng4674