clean up shipping modules for easier $final_shipping_cost

Adds consistent variables weight, total and count from cart, reducing redundant repeat calls of cart object methods (in some, but not all, files)
Also consolidates these and other calculations into $final_shipping_cost var
<a href='#crh-start'></a><a href='#crh-data-%7B%22processed%22%3A%20%5B%22https%3A//github.com/zencart/zc-v1-series/pull/132%23issuecomment-52430560%22%2C%20%22https%3A//github.com/zencart/zc-v1-series/pull/132%23issuecomment-52781771%22%2C%20%22https%3A//github.com/zencart/zc-v1-series/pull/132%23issuecomment-52783814%22%5D%2C%20%22comments%22%3A%20%7B%22General%20Comment%22%3A%20%7B%22html_url%22%3A%20%22https%3A//github.com/zencart/zc-v1-series/pull/132%23issuecomment-52430560%22%2C%20%22comments%22%3A%20%5B%7B%22body%22%3A%20%22Refactoring%20appears%20to%20be%20consistent%20throughout.%22%2C%20%22created_at%22%3A%20%222014-08-17T18%3A36%3A23Z%22%2C%20%22user%22%3A%20%7B%22avatar_url%22%3A%20%22https%3A//avatars.githubusercontent.com/u/404472%3Fv%3D2%22%2C%20%22html_url%22%3A%20%22https%3A//github.com/drbyte%22%7D%7D%2C%20%7B%22body%22%3A%20%22%3A%2B1%3A%20%22%2C%20%22created_at%22%3A%20%222014-08-20T14%3A00%3A43Z%22%2C%20%22user%22%3A%20%7B%22avatar_url%22%3A%20%22https%3A//avatars.githubusercontent.com/u/227354%3Fv%3D2%22%2C%20%22html_url%22%3A%20%22https%3A//github.com/zcwilt%22%7D%7D%2C%20%7B%22body%22%3A%20%22If%20I%20didn%27t%20know%20the%20reasons%20why%20those%20commented%20lines%20were%20left%20in%20there%2C%20I%27d%20say%20take%20them%20out.%20%5Cr%5Cn%5Cr%5Cn%3A%2B1%3A%20%22%2C%20%22created_at%22%3A%20%222014-08-20T14%3A15%3A53Z%22%2C%20%22user%22%3A%20%7B%22avatar_url%22%3A%20%22https%3A//avatars.githubusercontent.com/u/404472%3Fv%3D2%22%2C%20%22html_url%22%3A%20%22https%3A//github.com/drbyte%22%7D%7D%5D%2C%20%22title%22%3A%20%22General%20Comment%22%7D%7D%7D'></a>
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- [x] <a href='#crh-comment-General Comment'></a> <img src='http://www.codereviewhub.com/site/github-completed.png' height=16 width=60>&nbsp;<b><a href='https://github.com/zencart/zc-v1-series/pull/132#issuecomment-52430560'>General Comment</a></b>
- <a href='https://github.com/drbyte'><img border=0 src='https://avatars.githubusercontent.com/u/404472?v=2' height=16 width=16'></a> Refactoring appears to be consistent throughout.
- <a href='https://github.com/zcwilt'><img border=0 src='https://avatars.githubusercontent.com/u/227354?v=2' height=16 width=16'></a> :+1:
- <a href='https://github.com/drbyte'><img border=0 src='https://avatars.githubusercontent.com/u/404472?v=2' height=16 width=16'></a> If I didn't know the reasons why those commented lines were left in there, I'd say take them out.
:+1:


<a href='https://www.codereviewhub.com/zencart/zc-v1-series/pull/132?mark_as_completed=1'><img src='http://www.codereviewhub.com/site/github-mark-as-completed.png' height=26></a>&nbsp;<a href='https://www.codereviewhub.com/zencart/zc-v1-series/pull/132?approve=1'><img src='http://www.codereviewhub.com/site/github-approve.png' height=26></a>&nbsp;<a href='https://github.com/zencart/zc-v1-series/pull/132'><img src='http://www.codereviewhub.com/site/github-refresh.png' height=26></a>
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