Improve the LazyCat server.

Improve the LazyCat server.  Make the server work as a daemon and
split UI and the server part.  Make UI communicate with the server
through the well-defined protocol, so it become more
straightforward and flexible.  Improve the module hierarchy.  Move
all UI-related sources to ui directory.  Add a CLI for LazyCat.

* scheme/config.scm, scheme/diff.scm, scheme/host.scm,
  scheme/host-list.scm, scheme/logger.scm: Move to server/scm.
* lazycat-gtk.sh: Move to the ui directory.  Rename to
  lazycat-gtk.
* scheme/lazy-gtk-cat.scm: Move to ui/gtk.  Move all GTK-related
  stuff to ui/gtk.
* server/scm/lazycatd.scm: New file.
* ui/lc: New file.
* ui/cli/pretty-format.scm: New file.
* server/scm/protocol.scm: New file.
* server/server.c: Don't start the Guile shell -- run the lazycatd
  instead.