fixed GRADLE-3094: Scala plugin doesn't work when Gradle is run with Java 8

- Note that according to Scala release notes, latest Scala (2.11.1) doesn't really support Java 8 yet. Even when switching our integration tests to Scala 2.11.1, Scala compilation would fail with `VerifyError`s when running with Java 8.
updated preconditions and target scala versions for scala integration tests
Moved some stories out of the 2.0 spec, to done or the 3.0 spec.
Removed test that is no longer required.
Removed duplicate int tests.
Give the scala int tests a little more permgen.
Changed AntScalaCompiler to handle java 8 as a target.
Some tweaks to ScalaDoc constructor and method signatures.
Some user guide edits.
Mention that java 6 is required to run Gradle.
Mention that build scripts should be encoded using utf-8.
Javadocs.
Added some notest to release notes.