Coinbase Full Implementation & Demos

All the demos are working, but I haven't completely tested merchant orders and subscriptions as I need to set up an additional user.  I went with the weird nested classes for the dto's to match naturally with coinbase's weird nested json.

The adaption to a Ticker is a bit forced.  Do you think it would be better  to just throw a not supported exception?

I will be adding javadocs for the service classes and unit tests next...seriously need to improve my TDD mindset.