merge: Define types for more flags/bitfields

 * imap: rename constants to match capability strings
 * smtp: convert capability enum to flags
 * add typedef for ImapCapFlags
 * add typedef for SmtpCapFlags
 * add typedef for AnsiFlags
 * add typedef for CheckFlags
 * add typedef for MhSeqFlags
 * add typedef for AclFlags
 * add typedef for HashFlags
 * add typedef for MixCapFlags
 * add typedef for CliFlags
 * add typedef for SelectFileFlags