DATAJPA-606 - Improve handling of empty arrays and collections in query parameters.

Introduced potentiallyConvertEmptyCollection method to PersistenceProvider for provider specific handling of empty collections. Special handling is performed for Hibernate and EclipseLink. Conversion is performed in ParameterMetadata.prepare(..). Renamed ParameterMetadataProvider.accessor to bindableParameterValues.

Original pull request: #123.