Moved product JS to external file (mostly)

- Move majority of `product.liquid` JS into `shop.js.liquid`
  - In order to use `shop.js.liquid` cache'd selectors, the remaining JS is moved to `theme.liquid` so it runs after `timber.init` is fired.
  - Is it worth making a snippet, or does it look fine at the bottom of theme.liquid?
- And removed some console.logs (blame @Tetsuro)

cc/ @stevebosworth @mpiotrowicz 
should these be saved to timber.cache? Otherwise, since all are product related, they can also be saved to a single `productCache` obj or use a `product_` naming convention? Not sure any of these are needed, just wondering if they might help distinguish these are being product-specific