Refactor http codebase

This change-set tries to optimise the way the http related code is organised for better readability and extensibility. It uses streadway/handy as the JSON based logging middleware and in the same fashion implements a metrics middleware to expose prometheus based telemetry.

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/cc @grobie @peterbourgon @bernerdschaefer 
Ah, I see! Yeah, I imagine that covers all the bases. Carry on :)