Fix for Issue #17: allEntries on schemas with new lines (JSON-ified)

Integrated google-gson for more reliable serialization over the wire.
Added tests for JSON.
Client tests now submitted to persistence/multi-line tests.
No problem. Also take a look at this part of jersey docs:
https://jersey.java.net/documentation/latest/user-guide.html#providers-selection
This explains how content-type determines the choice of serialization.

We would probably have to return a `Response` object with the actual value to be serialized set as entity and response type set accordingly (to drive the above process).

If this (all the jersey plumbing) turns out to be too involved (which may very well be the case), the current (proposed) implementation may look more attractive. But I think it's worth to at least explore the more centralized approach.