merge: Define types for all of the flags/bitfields.

Being 'C' this doesn't add any type safety, but it does make the code far more legible.<Paste>

 * add typedef for ConfigDumpFlags
 * add typedef for ConfigRedrawFlags
 * add typedef for MuttFormatFlags
 * add typedef for HookFlags
 * add typedef for ImapOpenFlags
 * add typedef for ImapCmdFlags
 * add typedef for MuttAccountFlags
 * add typedef for CompletionFlags
 * add typedef for TokenFlags
 * add typedef for MuttRedrawFlags
 * add typedef for MuttThreadFlags
 * add typedef for OpenMailboxFlags
 * add typedef for MsgOpenFlags
 * add typedef for PagerFlags
 * add typedef for SendFlags
 * add typedef for StateFlags
 * add typedef for KeyFlags
 * add typedef for SecurityFlags
 * add typedef for CopyHeaderFlags
 * add typedef for CopyMessageFlags