WooCommerce Storefront Powerpack 1.6.3

* Enhancement - Header Customizer: Add support for floating elements and empty rows.
* Enhancement - Designer: New "Font Weight" select box for granular control over your typography.
* Fix - Add back Storefront header wrappers to the "Distraction Free Checkout" option header area.
* Fix - Update Sticky Header `z-index` value to stop overlapping with the product image full screen lightbox.

* Tweak - Use original string when homepage section title is left empty. Useful for multi language sites.

* Fix - Ensure that custom color is applied to star ratings.
* Fix - Add new loop thumbnail selector to Designer.
* Fix - Improvements to Storefront Designer CSS output for increased CSS specificity.
* Fix - Filter WooCommerce image sizes to override values set by Storefront.