A bunch of small changes after gson addition (mostly android)

1. remove gson from main classpath (build.xml).
2. upgraded gson jar from 2.2.4 to 2.3.1 and keep version number in the name of the jar.
3. fixed android test build. (added gson jar and tests)
4. code tidy, fixed some generics related warnings.
5. enhanced messages for android test run. (build.xml)
6. removed support for MemoryFile in Android version.