Cart Class File Cleanup and Function Deprecation

Was about to do a tiny bit of work in the cart class part of the cart.class.php and noticed that the file would benefit from a little cleanup before I made changes. The next PR will be quite a bit easier to read without having to weed through much of what didn't change.

* This commit does not have any logic changes other than the deprecated functions noted here.
* the template functions were moved to a distinct file.
* The cart class is now the only thing in the cart.class.php file.
The google checkout functions have been deprecated. Note that one google checkout function is a part of the cart class.  That function has been deprecated in place.