Make the plugin use VIP Go file service when running on the platform

We should not rely on Photon in case the plugin is running on the VIP Go platform, as the VIP Go File service as it's capable of performing the same transformations and is the preferred way to manipulate images for the sites on the platform.

Since the VIP Go File service is Photon-like, and uses the same params, it should be rather straightforward.

The vipgo-helper.php file seems to be the easiest mean of platform detection and place where the behaviour modifying code can live.

Start with vipgo-helper.php to understand the existing platform-detection behavior and locate how the plugin currently relies on Photon. Compare the VIP Go File service's Photon-compatible parameters, then verify that platform sites use that service while other environments retain the existing behavior.

Written by the indexing model from the issue text.