Added predefined imap-search criterias

I've noticed that "imap.gmail.com" returnes no messages when using `MailClient::MessageList`, although parameter `MessageCount` using `MailClient::FolderInformation` is non-zero. I don't known why, but I believe it is some sort of GMail/imap quark (`MessageCount` is actually much large than what the Gmail webmail client reports). 

Anyways, I've found a workaround, which was to use the predefined imap search query 'ALL' which MailSo do not currently support. 

This pull-request add support for all predefined imap search queries.