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

Hi Hugo,

The PR extends from https://github.com/hhuijser/liferay-plugins/pull/184.

I find InternetAddressUtil.toString(Address[] addresses) method is used for generating emailAddress format when update or add message in mail_message table. Please refer to IMAPAccessor.storeEnvelopes() and IMAPMailbox.saveDraft() in mail portlet. The current "comma" delimiter between email addresses was generated in this method InternetAddressUtil.toString(Address[] addresses). 

I also check the InternetAddressUtil.java log and find we used "StringPool.COMMA+StringPool.NBSP" as delimiter before applying LPS-30185 fix. For the current fix, if we use "space" instead of "&nbsp;" and the LPS-30185 won't occur.

Could you please help check this fix?

Thanks,
Hai