=pro Fix doc build of java only projects

* javadoc complains on the -target flag for projects with only java sources
* found solution here: https://groups.google.com/forum/#!topic/simple-build-tool/I75AODwFlH0
=pro Exclude osgi samples from zips, (fails, no content)
Merge pull request #1893 from akka/wip-doc-build-patriknw

=pro Fix doc build of java only projects