Adds support for Scala 2.12
Bumps to master sbt version
Adds 2.12 support in ScalaInstallationTests
Adds 2.12 support to ClasspathTests
Adds support for 2.12 in breakpoint tests
Specialize Scala 2.11 feature for 2.11 and 2.12 build

The Scala 2.11 feature for the 2.11 build has a reference to the bundled
Scala 2.10 jar. We don't want this reference for the Scala 2.12 build.

This will be removed when the need of the bundled Scala 2.10 jar is fixed.
Fixes shortString method for version <= 2.9

And move common code in CompilerUtils
Merge pull request #727 from skyluc/2.12-support

Adds support for Scala 2.12