Adjustments needed in the New Sync Page

[felipeelia]

This issue follows the work done in #2448. Items that still need to be done:

• assets/css/sync.css could make some usage of CSS vars (1 h) Update to use CSS vars #2561
• --offset parameter is not working as expected on EP.io Fix/cli offset #2591
• Errors count is not correct yet. If an "Entity too large" request is fired, the count is still showing "0". Same for the count of errors line for individual posts errors Simplify the errors count #2590
• Sync page should show the progress of WP-CLI sync (1.5 h) Show WP-CLI progress on sync page #2564
• When an indexing is stopped by the WP-CLI command we should show a message on the output (Show a message when an indexing is stopped by the WP-CLI command #2549)
• Fix the AJAX URL when the EP is activated in a subsite (that is not the main site) Fix AJAX URL on subsite #2501
• In includes/classes/IndexHelper.php, $start_date_time->format( 'D, F d, Y H:i' ) should be internationalized, so it can be localized later (Add i18n to index start and end date format #2548)

[felipeelia]

Now that all items were addressed, this can be closed.