Moving Kite Dataset API info from old guide per CDK-753.

Link to the old guide from which this came. This is just shards of information brought forward so they're not lost. This info should be woven into the samples before 1.0.

http://kitesdk.org/docs/current/kite-data/guide.html
I don't think it is accurate to say, "the `Datasets` class is the workhorse of the Kite Data API". Instead, it is the starting point to the Kite API. You will almost always start working with Kite by loading a dataset with the `Datasets` methods.