apply_filters for values in $javascript_array

Create filters for values sent to SimpleReach: `sranalytics_title`, `sranalytics_url`, `sranalytics_date`, `sranalytics_channels`, `sranalytics_tags`, and `sranalytics_authors`.

Allows sites with unconventional setups to send the correct data. For example, when using [Co-Authors Plus](https://github.com/Automattic/co-authors-plus) for post attribution, the following filter could be used to send author data:

```php
<?php

/**
 * SimpleReach Analytics and Co-Authors Plus
 *
 * @uses get_coauthors
 * @param array $authors
 * @return array $authors
 */
add_filter( 'sranalytics_authors', function( $authors ) {
	if ( ! function_exists( 'get_coauthors') ) return $authors;

	$authors = array();
	$coauthors = get_coauthors( get_the_ID() );

	foreach ( $coauthors as $coauthor ) {
		$authors[] = $coauthor->display_name;
	}

	return $authors;
} );
```