Use BEM style CSS selectors in default templates

[jedateach]

I think the shop module could benefit from using the BEM style to better name components of each template. I find myself rewriting class names etc every time I work on an ecommerce project. If I can avoid than, then win :+1:.

Doing this will also help avoid any conflicts with other project css.

Part of this work would be to strip out all the ID tags in templates.

Of course this would break some visual backwards compatibility, so I'm milestone it v2 for now.