cross build against scala versions 2.10.3 and 2.8.1

This pull request contains the changes necessary to support Scala cross-building with Gradle using versions 2.8.1 and 2.10.3.  Gradle will suffix all Scala modules with the appropriate Scala version suffix (e.g. cluster becomes cluster_2.8.1 and cluster_2.10).  Clients that consume Norbert artifacts will have to update the names used in their dependencies to include the suffix.  To produce _2.10 artifacts, the crossBuild property needs to be set to true (e.g. gradle -PcrossBuild=true build) otherwise only tasks for the default Scala version (2.8.1) will be executed.  Cross-building should be enabled when publishing artifacts but otherwise you may wish to keep it disabled (e.g. if generating an IDE project or if you are iterating on code and don't want the build to take 2x as long)