v3.5.3: Bugfixes

This release contains corrections for the following GitHub issues:

#231: Correct PHP Parse error when payment methods "collect credit card data on-site".
#232: Correct PHP Warning logged by shopping_cart template.
#233: Correct products' model alignment on listing pages.
#234: Add language constant added for zc158 that doesn't exist in zc157.
#235: Add missing text 'lead-in' for products' quantity on listing pages.