Suggestion: remove duplicates from list of child themes

In the themes list, if a theme is a parent for a child theme that is active on multiple blogs, the child theme is listed for each blog where it is active, resulting in duplication.

Suggested fix, in class-add-theme-list.php, call array_unique on result list before returning:

	
/**
	 * Gets an array of themes which have the selected one as parent.
	 *
	 * @since  21/02/2015
	 *
	 * @param String $theme_key The key of each theme.
	 *
	 * @return array
	 */
	public function is_parent( $theme_key ) {

		$blogs_themes = $this->get_blogs_themes();
		$parent_of    = array();

		/**
		 * Provide the data to the Theme of each site.
		 *
		 * @var array $data
		 */
		foreach ( (array) $blogs_themes as $blog_id => $data ) {

			$template = FALSE;
			if ( array_key_exists( 'template', $data ) ) {
				$template = $data[ 'template' ];
			}

			if ( $template !== $data[ 'stylesheet' ] && $template === $theme_key ) {
				$theme       = wp_get_theme( $data[ 'stylesheet' ] );
				$parent_of[] = $theme->get( 'Name' );
			}
		}

		return array_unique($parent_of);
	}