[Snails] FolderDescr::Row().
[Snails] Keep Folder2Descr map.
[Snails] Support message counts in FoldersModel.
[Snails] Code style fix.
[Snails] GetFolder() may return nullptr now.
[Snails] Kludge for gmail (it's not a real folder after all).
[Snails] First sync IMAP folders.