Unnecessary HEAD requests

[cristimirt]

The plugin is checking for the existence of a certain css file on every admin page load, via the FontAwesome_SVG_Styles_Manager::ensure_svg_styles_with_admin_notice_warning() function, and that's reasonable.
However, this function is called on the init hook if is_admin() returns true, which happens on every ajax request, be it from the backend or the frontend of the website. This can quickly turn into hundreds or thousands of HEAD requests per minute, which are not needed and could cause issues with too eager or misconfigured firewalls.

I'd suggest checking for wp_doing_ajax() at the beginning of the FontAwesome::initialize_admin() function, and return early if it is an AJAX request.