Add dependency on scala-xml Scala 2.11 module to templates project.

Add conditional (dependent on Scala version) dependency on scala-xml
module to the templates project. This way Play project has correct
dependencies when either Scala 2.10 or 2.11 is used.
Remove use of scala.ScalaObject

ScalaObject has been removed in Scala 2.11 and it was an implementation
detail that other projects shouldn't rely on. It looks like Play was using
ScalaObject to locate scala-library.jar. Let's switch to scala.Predef for
that purpose. It is a class that is likely to stay across all future Scala
versions.
Switch asJavaListConverter -> seqAsJavaListConverter

asJavaListConverter has been deprecated since 2.9 and got removed in 2.11.
Merge pull request #2470 from gkossakowski/scala-2.11

Scala 2.11 compatibility