Correct structure for updating

This applies to all mode of block: image, text, and product. Product
block needs an adjustment tho
Populating related data when saving product

Previously, wcng only stores product ID upon syncing. Now it populates
related data (title, price, image, permalink) upon syncing so
wcng_date() shouldn’t populate those data when the newsletter is viewed.

UX improvement:
- Blurring the block when it is synced