Added cross-compilation for 2.10 / 2.11 Scala version

Added cross compilation capability to build and made changes required for it to build on both Scala runtimes. 

This also actually solves the problem https://github.com/anvie/blueprints-scala/issues/23

There is one question left:
* how to make it available through maven central ?
this got removed from Scala and was actually already deprecated in 2.10 http://www.scala-lang.org/api/2.10.4/index.html#scala.ScalaObject