[Snails] Message::{G,S}etID() -> {G,S}etFolderID().
[Snails] Request full header.
[Snails] Added MessageId.
[Snails] Added InReplyTo() to the message.
[Snails] Parse InReplyTo.
[Snails] Check for null mbox.
[Snails] Refactored common stuff into ToMessageSet().
[Snails] AccountThreadWorker::deleteMessages().
[Snails] Account::DeleteMessages().
[Snails] MailTab::GetSelectedIds().
[Snails] Action for removing messages.
[Snails] Don't forget to expunge the messages.
[Snails] Moved msg actions to the tab toolbar.
[Snails] Code style fixes.