CDK-556: Change the default data model for reflection to ReflectData.AllowNull

* The fix also includes two tests, including one to check the behavior of
  using AllowNull with a PoJo that has primitive fields.

Closes #209
Throw descriptive exception when JDK is not installed.
Merge pull request #214 from smola/fix/jdk-missing-warning

Throw descriptive exception when JDK is not installed.
CDK-670: Rename CLI command dataset to kite-dataset.