Add profile page for event loop thread #2144
We have nice statistical profiling for the worker threads of each worker that is visible from the bokeh diagnostic pages. However it would be nice to also get this same kind of information about the main administrative thread within the scheduler and workers themselves. This will help us to understand performance costs generally and tune the scheduler and worker codes.
This PR copies and modifies the profile code to operate on each event loop and provides a new route (currently not advertised) on the dashboard. This helps us to understand the costs of things like asyncio and how they affect our general performance.