Fix #974: Implement java.util.UUID

Re-implementation of java.util.UUID in Scala in order to be smoothly integrated with scala-js.
This code is based on the openjdk's one which check against version 1.(http://hg.openjdk.java.net/jdk8/jdk8/jdk/file/687fd7c7986d/src/share/classes/java/util/UUID.java),

By the way, should we mentioned it in the header?