"Built-in" Chat using WordPress comments and WP API could use Server-Sent Events instead

[fabacab]

Right now, the default chat system uses the WordPress commenting system to implement the incident chat functionality refreshed through traditional polling. Instead, let's use HTML5 Server-Sent Events (spec) to reduce the HTTP overhead since we are actually only communicating in one direction at a time (receiving/server-to-client on the chat template, and sending/client-to-server on the chat form part).

Note that Microsoft browsers still don't support EventSource, so we'll need to fall back to the current polling mechanism if we are running on Internet Explorer or Edge.