Better data hiding in auth code. Isolate Gson usage.
*  finalize a bunch of members in client classes.
*  make auth client private in BaseClient.
* clean up some imports.
* remove unused exception class
* instill a proper exception inheritance hierarchy.
* make member clients private in Client.java
* make more members final in ClientResponse and HeartBeater.
* remove unused method in Utils.
meh. prepend this to the members.
Merge pull request #15 from racker/RSR-21/idiomatic

Client code cleanup