Check that products_id is an integer and/or with curly braces for attributes (+2 squashed commit)

Squashed commit:

[a2ed9dc] Fix typo

[bb722c7] check first that products_id is not null, then that is a positive integer and without letters
Check only if products_id returned from application top is a valid int or null
code clean
Add comment
Remove int conversion of products Id as it is already converted in application top
Inverting products_options array
Simplify product class. Now is possible to call every element of the product array. Example $product->get('products_name');
Fix comment
Move product breadcrumb to its class
Remove unnecessary class and module option
Fix typo
Merge branch 'product_class' of https://github.com/acidvertigo/oscommerce2 into product_class