Adds scalastyle plugin to Cypher's pom.xml

o scalastyle is *not* run by default for now
o run it explicitly with mvn -DscalaStyle scalastyle:check
o run it as part of verify with mvn -DscalaStyle verify
o config is in etc/scalastyle_config.xml and needs tweaking
Merge pull request #732 from boggle/2.0-with-scalastyle

Adds scalastyle plugin to Cypher's pom.xml