[development] Move all core modules into their own directories.

[sime]

Dries Buytaert wrote:

> One of the things I'd like to see happen, is that we move away from
> the theme_ functions, and that we make PHPTemplate files for each
> theme function.  So, if you are a designer and you want to theme a
> part of Drupal, you just copy the template from module/foo/bar.tpl.php
> to your theme directory, and you start hacking away at it.

:drool:
That sounds good.