Log how much data was sent to the client in loaders/actions

[alexdotpink]

It would be incredibly useful to know how much data (in KB) the server is sending to the client on every request, both for loaders and for actions.

[AlemTuzlak]

I would love to do this and I'll move this to discussions because at the moment I'm not sure if I can read data without crashing the server. I'll add this in if I figure that part out!