[FRAME-176]: Delay Events Until Shutdown

[tarecord]

This adds functionality to cache all events for the request until the shutdown action. Then during shutdown each event request is sent in a similar fashion to how we send the telemetry data.

1. A request is sent to the ajax endpoint
2. A new request is created during the ajax request to actually send the event to the server

This should keep the user from needing to wait for the requests to send, but it does not prevent the server from being overloaded if a plugin sends a large number of requests on each page load.

[ChrisMKindred]

This is a great first step to the fix. The lift would be very low to add an events endpoint to the server and send all the events in one request. As rare as it might be, the event cache could be large, and calling an admin-ajax request for each is inefficient.