Enforced java/scala compiles using atleast 1.6

Noticed that the zip file is compiled using a Java 7 javac. Added scalacOptions (incase there are scala files in the future) and javacOptions to ensure the jars compiled are compatible with Java 6.

You may notice a warning from SBT about the bootstrap classpath. I think this is because I haven't specified a specific rt.jar (located in jre/lib). It will default to the right one anyway.