Clean up functions for both store and site

[drewbaker]

Here are some things I need to clean up:

• [ ] Remove inline arrays from second image function (use $args).
• [x] Remove use of global in meta box functions
• [x] Correct save key for second image
• [x] Add get_second_post_thumbnail() function to boilerplate from Kinfolk
• [ ] Update production variation function to respect attribute names (as done on Kinfolk). Build in some caching perhaps?
• [x] Update template to use price_html function as per Kinfolk or write something better that accounts for display price (price + tax), sale, free, discount, currency type etc.
• [x] Include get_product_brand function in boiler plate? Build in some caching? Maybe better to put all these onto Stackoverflow?
• [x] Probably worth making store filters get applied in a certain order always, probably top down, so it goes clothing+shirts+kinfolk instead of clothing+kinfolk+shirts? Maybe? Maybe better to apply them in the order they are clicked, as currently done.

[SaFrMo]

@drewbaker Updating this list to be as current as possible

[drewbaker]

We can remove all store stuff, I don't think we are going to use WooCommerce ever again now that we have Shopify plugin.