Rewrite cod_sponsor_sales to work in D7

cod_sponsor_sales  has many D6 dependencies and therefore could not be loaded in D7.  This pull request updates this module so that it will work in D7.  The basic functionality is now available, though there may still be some additions necessary.

In summary, these changes use the commerce_node_checkout module to create sponsorship products dynamically based on the sponsorship level vocabulary.

A user can only add one sponsorship item at a time, and attempts to and an attempt to add another will clobber the first.