extract theme-roller into a bundle

@senny because of the improvements of the `deftheme` macro in emacs 24, I think there should be the possibility to choose between theme-roller or themes served via `deftheme`. There are already a lot of nice themes out there.

What do you think?
instead of double nested conditionals you can use `or` and/or `and` to build more complex conditions. I suggest changing `unless` to `when` as well. As it is easier to read with complex conditions.