More message-index functionality.

  The scrolling up/down of the message-list works.  We've also
 rebound "/" so that it works for both maildir-mode and index-mode.
  We use libmimetic to parse messages now.

  This means we can format the display of messages in the index-view.

  The lua primitive `index_format` is used to specify a simple
 format-string to display.
  Removed dead/obsolete/debug code.

  The main driver is now wonderfully simpl.
  Work with the message-indexes too now.
  Added new primitives for scrolling message-lists.
  Added primitives for index-scrolling, etc.
  Drawing indexes works.
  Updated to be neater.
  Reformat.