Updating Groovy to 2.3.0 #27

To get the newer groovy-eclipse-compilier you need to set up a mirror
for aduna softwares repo like:

~/.m2/settings.xml

<mirror>
  <id>ibiblio.net</id>
  <url>http://www.ibiblio.net/pub/packages/maven2</url>
  <mirrorOf>http://repo.aduna-software.org/maven2/releases/</mirrorOf>
</mirror>

Had to fix a few error with type checking and static compiling when
doing calls between java and groovy. The tests are OK but I'm not 100%
comfortable..