Add ability to handle select values based on the definition returned type

• Type: Task
• Status: Closed
• Priority: Minor
• Resolution: Completed
• Affects Version/s: None
• Fix Version/s: Master
• Component/s: Forms
• Labels: None
• Priority Level: Low
• Sprint: Forms #41 - May 2 - 12
• Git Pull Request: https://github.com/liferay/com-liferay-dynamic-data-mapping/pull/192

There's a possibility to define a String return type for select field types. However, internally Forms stores the select value as JSON Array because select could have multiple values.

This task aims to normalize the JSON array info in the DDMFormInstanceFactory creation. If it's a single value it returns the single value, if it's multiple is joins the values into a comma separated value.