Security Hardening, Gallery & Legacy Theme Fixes

Added a nectar_ignore_salient_meta filter to read back an individual legacy Salient page setting, per key and per post
Added a notice with a one-click license transfer when a site moves to a new domain

Fixed a security issue by adding stricter permission checks
Fixed a security issue by hardening how image markup is escaped
Fixed core Gallery blocks collapsing to one image per row when a small block gap was set
Fixed the transparent header being forced on pages migrated from Salient, even with the Nectar Blocks per-page toggle turned off
Fixed oversized slide padding in the Company at a Glance template carousel
Fixed the Template Library failing to load in long-running editor sessions until the page was reloaded
Fixed a site deregistered from the account portal re-activating itself on its next update check

Updated the Ticker and Scrolling Marquee blocks to keep animating when the browser asks for reduced motion