* Rename customizer JS files to customize-preview.js and customize-controls.js to align with the core file naming and make it clearer where each file runs.
* Only show the colorscheme_hue control when there's a custom color scheme.
* Update preview JS handling for revised front page section handling, see below.
* Remove all references to "Theme Customizer" in code comments. It hasn't been called that since before 4.0.
* Clarify the purpose of the JS files by updated the code comments in the file headers.
* Improve code readability.
* Make the arbitrary number of front page sections filterable, for UI registration and output.
* Rename twentyseventeen_sanitize_layout to twentyseventeen_sanitize_page_layout to be clearer about what it sanitizes in case child themes or plugins consider reusing it.
* Rename page_options setting/control to page_layout as that's more reflective of what that option does; and again, helps for potential extensions.
* Make the page layout option contextual to pages and the sidebar being inactive, as the option only applies when there is no sidebar (per its description).
* Condense options into a single section.
* Add selective refresh for front page sections.
* Locate active_callback functions within customizer.php so that they're easier to find when editing customizer registrations, similarly to sanitize callbacks.
* Adjust the styling for placeholders for panels that aren't active.
* Ensure that the new visible edit shortcuts don't have any issues.
Props celloexpressions.
Fixes#38426.
Built from https://develop.svn.wordpress.org/trunk@38986
git-svn-id: http://core.svn.wordpress.org/trunk@38929 1a063a9b-81f0-0310-95a4-ce76da25c4cd
This adds the ability for themes to add support for videos in custom headers
by passing `'video' => true` as an argument when adding theme support for
custom headers.
Custom video headers are managed through the “Header Visuals” (i.e. “Header Image”)
panel in the Customizer where you can select a video from the media library or set a
URL to an external video (YouTube for now) for use in custom headers.
This introduces several new functions:
`has_header_video()` – Check whether a header video is set or not.
`get_header_video_url()` – Retrieve header video URL for custom header.
`the_header_video_url()` – Display header video URL.
`get_header_video_settings()` – Retrieve header video settings.
`has_custom_header()` – Check whether a custom header is set or not.
`get_custom_header_markup()` – Retrieve the markup for a custom header.
`the_custom_header_markup()` – Print the markup for a custom header.
And a new file, `wp-includes/js/wp-custom-header.js` that handles loading videos
in custom headers.
This also enables video headers in the Twenty Seventeen and Twenty Fourteen themes.
Props davidakennedy, celloexpressions, bradyvercher, laurelfulford, joemcgill.
Fixes#38172.
Built from https://develop.svn.wordpress.org/trunk@38985
git-svn-id: http://core.svn.wordpress.org/trunk@38928 1a063a9b-81f0-0310-95a4-ce76da25c4cd
