[Launch Your Store] Add generic function to determine if URL is a store page

[chihsuan]

Issue description

Add a generic function for determining if URL is a store page so that we can keep store pages in “Coming Soon” mode while keeping the rest of the site live.

Accept criteria

• function should return true if URL is a store page, return false, otherwise

Store pages are defined as:

• Shop Page
• Cart Page
• Checkout Page
• My Account Page
• Terms and Conditions Page
• Privacy Policy Page

(the above page IDs can be determined from WooCommerce Settings)

Additionally, the following autogenerated pages should be included:

• Product Categories (taxonomy=product_cat)
• Product Tags (taxonomy=product_tag)