Scale to events per second in statistics graphs

Hi Keith,

Can you please take a look at this change?  I find operations / second much easier to think about (it means the "wait" config isn't a factor in interpreting the graphs), but there are a few statistics that don't make sense to scale (e.g., number of bytes in the cache, number of files currently open).  The solution isn't great, but I haven't come up with anything better.

Thanks,
Michael.