modularizing server and introduce cli example.

Following up from https://github.com/GoogleCloudPlatform/google-cloud-datastore/pull/50, this sent the server files to a new `/server` directory, as well as introduced a CLI example a little more sophisticated than the one from the earlier PR.

An easier to look at representation: https://github.com/stephenplusplus/gcloud-node-todos

![screen shot 2014-09-26 at 3 13 33 pm](https://cloud.githubusercontent.com/assets/723048/4426388/08dfd2ca-45b3-11e4-9f7b-b95a6b08d8e1.png)
The transaction may have been overkill. The more important part was sending one Datastore API request vs several. I think to remain true to how the TodoMVC FE works, a special case shouldn't be added. I'll just make individual requests the same way the web UIs will work.