Added the initial Cart and CartItem models.
Added routing, controllers and views for the Cart and CartItem models. Improved validation for the CartItem model so CartItems can be removed by specifying a quantity of zero.
Added styling to the new cart elements. Formatted the css manifest file with SASS so the bootstrap elements can be used with SASS helpers.
Merge branch 'develop-cart' into develop
Added rvmrc config to the Pow development server configuration because Pow will no longer read the rvmrc files in future versions.