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

[Gabor Hojtsy]

Neil Drumm wrote:
> Dries Buytaert wrote:
> 
>> The disadvantages:
>>  * PHPTemplate would become more dominant.  It's not clear how this
>> can co-exist with other theme engines.
> 
> I would actually be okay with removing the whole engine system and
> simply doing PHPTemplate only. Sure theme engines are a nice feature,
> but how many are maintained and what % of themes are PHPTemplate?

Neil, there were some points that supporting plain PHP function based
themes are going to be continued. They can be a lot faster then
including 20 PHP template files just to build a page.

Goba