Versions API

-Added GenVersions generator to generate Versions.scala that contains the version and buildForScalaVersion.
-Added version and buildForScalaVersion to org.scalatest and org.scalactic package object by calling Versions object.
-Removed AppVersion and ScalaVersion from ScalaTestBundle.properties, and make AboutJDialog and Runner to use version and buildForScalaVersion in org.scalatest package object instead.