Create a new sub-tool to report the latency difference between 2 event streams

[peterbarrow]

As part of the performance work, a question was asked about the latency difference between the event stream coming straight from the core and the event stream distributed from the data node. Add a tool which will subscribe to 2 different event streams and report which one is ahead/behind and by how much.

This will be useful to see how much expected latency is added going through the datanode and also to see which of the many public datanodes available after go live will give you the fastest event stream.