Attach sources and some fixes for apk extensions and play services

I'm still working on adding source code to all artifacts. Now I'm done with apk extensions and play services. There was also problem with bad path to resources for apk-expansion-downloader and change in SDK API required to build.

Because of this bug
https://code.google.com/p/android/issues/detail?id=50461
isn't possible to compile apk-expansion-zip-file  :-( .. so it is possible but it require never API and library will not work on pre API 12 devices :-(

I also was a problem with -P 4.2,with-javadoc switch. It not found path to generated platform javadoc so I change path defined in platforms/pom.xml. But I don't know where is problem now, because this works before with old path. So I commit it as separate commit.