Customize: Clean up docs and code style for customize changes in 4.7.

* Adds missing `resolve`/`fail` for promise returned by `loadThemePreview`.
* Adds missing jsdoc blocks and tags.
* Adds missing phpdoc and makes corrections.

See #37770.
Fixes #38908.


git-svn-id: https://develop.svn.wordpress.org/trunk@39345 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-customize-control.php

@@ -119,7 +119,7 @@ class WP_Customize_Control {
 	 *
 	 * @since 4.7.0
 	 * @access public
-	 * @var array
+	 * @var bool
 	 */
 	public $allow_addition = false;