Control-center redux

[Jonathan Blandford <jrb redhat com>]

There's been some debate as to what the next control-center should look
like, and how to get them ported as soon as possible.  I'd like to try
to open it up again in the hopes that we can get a solution soon.

The current plan is to ditch the current embedding app, and make all
'capplets' simple dialogs.  These would be launched from either the
panel menu, nautilus, or the simple shell.  Currently, all capplets link
to libcapplet.  We can either port them away from libcapplet, or modify
libcapplet as needed.  There are a couple reasons we might want to keep
libcapplet:

 * One-time support:  We can add this to the capplets easily.  Of
   course, with GConf being used, the problem of multiple instances of a
   config dialog goes down.

 * Enforcing of style guide:  I don't know how important this is, as
   social pressure and control of the code does a pretty good job of
   keeping things consistent.  Still, it might be useful to cut down on
   the number of bizarro third-party capplets.

 * Flexibility in the future:  If we decide that embedding wasn't such a
   bad idea after all, we have the flexibility to go back and add it
   without too much trouble.

Additionally, we need to decide what the basic capplet should look like.
We've been wanting to move to instant-apply for a while, but it's clear
there are cases where it's not going to work as well (such as the theme
changer, or eve the background selector) as the action is too slow.
Additionally, I'm pretty sure changing the mouse's acceleration while
trying to drag the slider is bad UI. (-:

Whatever we decide, it'd be good to decide soon, as we have a lot of
capplets to port, and the sooner we can start, the better.

Thanks,
-Jonathan