[development] Strip out theme functions into a .theme file

[Frando (Franz Heinzmann)]

I started working on this a bit.
I wrote a little script that uses some regular expressions to remove all 
theme functions from the .module files and put theme into a .theme file. 
This .theme file is included at the beginning of all .module files that 
have a .theme file.

More details and the extractor script can be found at the issue: 
http://drupal.org/node/76596

It's working greatly for me so far, I haven't found any bugs yet. Some 
reviews would be appreciated. I'd really like to get this into 4.8.

Regards,
frando