Images within Admin AJAX not handled

[mikeselander]

The Tachyon plugin currently doesn't handle any images served via admin-ajax by default. This leads to missed expectations whereby images loaded for the frontend via admin-ajax (infinite loading or load more functionality, for example) are only partially passed through Tachyon. The main image URL is not Tachyoned, but the srcsets are.

One could modify this behavior with the tachyon_disable_in_admin filter and custom logic, but I would expect the plugin to be able to do some default differentiation and tell whether or not it should handle images in an admin-ajax context.