LPS-45877 - Adding "comma and space" as delimiter between email addresses

Hey @hhuijser,

Attached is an update for https://issues.liferay.com/browse/LPS-45877.  Can you please review these backend changes?

"Please see Nate's comment from https://github.com/natecavanaugh/liferay-plugins-ee/pull/192#issuecomment-40001613 for more details.

I think "adding space between email addresses in the java class" is better.

If adding space is done on the JSP level, we need to handle with all used "to, cc, bcc" content in all jsp. If we save all formated content in "to", "cc" "bcc" field in mail_message table, we won't handle with it in all jsp." - @yuhai 

Please let me know if you have any questions.  Thanks!