Support CSRF Token in AJAX requests

[tmfink]

Currently, a JS snippet is inserted that rewrites forms to include the CSRF token. However, this does not include the token in AJAX requests (because they are done via JS, not an HTML "form" element.

In order to support this, JS would need to be inserted at the top of the page to override all JS functions that support requests.

https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest