Possibility to query an IMAP folder's size (in case IMAP Server [Dovecot] supports the X-SIZE STATUS fetch item)

In order to have that field available the new folder field size (id=318) has been introduced the provides the size of the content of a folder (in bytes) or -1 if unknown.

Only applicable for mail folders of the primary mail account and if property com.openexchange.mail.supportsMailboxSize has been configured to be true