Enable the validator's 'onlyNotNull' option.

This option has no effect if 'onlyDefined' is set to false.
Cleanup:  Validator plugin internal function name.
Add tests for validator's 'onlyNotNull' switch.
Fix validator 'onlyNotNull' test to use existing table columns.
Merge pull request #68 from jordan-ayers/topic/validator-options

Topic/validator options