Fix up examples to match documentation.

*  modified + issued are supposed to have accepted values of Date (YYYY-MM-DD)
*  accessLevel lists out Public, Restricted and Private as having capital letters

If this commit is accepted, and the JSON Validator accepts the commit in [Issue #6](https://github.com/project-open-data/json-validator/pull/6), then the JSON examples in the [metadata-resources](http://project-open-data.github.io/metadata-resources/) should pass the validations.

Neither of these changes includes the JSON changes that  jpmckinney + myself have been creating issues around, but I'd be happy to update the validator and examples if those are accepted as well.