Add scheduler utilization helper module.

Here is a little helper which can be used to get info about scheduler utilization, as per doc:

http://www.erlang.org/doc/man/erlang.html#statistics_scheduler_wall_time

Let me know if you are happy for this to be part of recon. For now, I'm keeping this as a separate module and in the form of a `gen_server`, but feel free to suggest changes.

Shall we include it in recon, I will update the recon doc before merging.